Stefan Rennick Egglestone

Brendan Walker

Joe Marshall

Steve Benford

Derek Mcauley

Analysing the playground: Sensitizing concepts to inform systems that promote playful interaction

Keywords: Playground, playful interaction, sensitizing concepts

Playful interaction in an important topic in HCI research, and there is an ongoing debate about the fundamental principles that underpin playful systems. This paper makes a contribution to this debate by outlining a set of sensitizing concepts which have emerged from an analysis of interaction in the playground; these help explain its appeal to children, and have been selected for their potential to inspire the design of future playful systems. These concepts have emerged from the analysis of material collected during a structured workshop which was organized by the authors, and which was attended by a group of experts. They have also been applied to the design of Breathless, a playful interactive system which has recently been deployed by the authors, and which represents an unusual evolution of the playground swing. The paper concludes with a number of reflections inspired by Breathless. These have been structured through the use of the concepts as an analytical tool.

Introduction

Playful interaction has been a topic of HCI research for some time, and a variety of authors have provided contributions that have helped shape design. Gaver, for example, has considered aspects of playful interaction that relate to ludic [START_REF] Huizinga | Homo Ludens: A study of the play element in culture[END_REF] activities such as exploration, invention and wonder [START_REF] Gaver | Designing for Homo Ludens[END_REF], whilst Bekker, Sturm and Eggen have emphasised the importance of both physical and social aspects of playful interaction [START_REF] Bekker | Designing playful interaction for social interaction and physical play[END_REF], suggesting a set of values that underpin them, and describing a set of systems that illustrate the application of these values to design. Although some studies have focused on playful interactions between children and computing technology [START_REF] Nielsen | Out of the box: exploring the richness of children"s use of an interactive table[END_REF], play is an activity that can be beneficial for humans of all ages, and there is a growing strand of research focused on design-led investigations into systems that exploit playful interaction to provide beneficial effects. A significant example is the use of gaming systems to promote whole-body interaction and rehabilitation for individuals who have acquired physical disability. Here, technological approaches have ranged from immersive virtual-reality systems [START_REF] Kizony | Adapting an immersive virtual reality system for rehabilitation[END_REF] to commodity gaming consoles such as the Nintendo Wii [START_REF]Online guide to the use of the Nintendo Wii in physical rehabilitation[END_REF], with the latter becoming regularly used by professional therapists to support individual rehabilitation in both clinical and domestic settings.

Within this broad area of research, the authors have previously pursued a series of design-led investigations that have been inspired by the theme-park environment, and which have resulted in the deployment of systems with which participants have demonstrated a variety of different types of playful interaction. In Fairground: Thrill Laboratory, a number of volunteers were fitted with a telemetry system that captured aspects of their experience on a thrilling ride and transmitted it back to a live audience [START_REF] Walker | Augmenting amusement rides with telemetry[END_REF]. Transmitted information included video of the rider"s face and quantifications of their physiological responses to the ride; observations and interview analysis have since revealed examples of riders using these systems in a playful way, either by choosing to perform to an unseen audience through the video feed, or by trying to play games with their own physiological response, in the knowledge that it was being observed and interpreted by others. More recently, we have constructed the Broncomatic, a novel, small-scale ride that rotates left and right in response to the direction of a rider"s breathing; this has been embedded into a strenuous, competitive game which encourages competitive social interaction between participants [START_REF] Marshall | Breath control of amusement rides[END_REF].

However, in tandem with such design-led interventions, we have recently engaged in research into the principles of systems that promote playful interaction, and a presentation of the outcomes of this research is the central contribution of this paper. Working within a framework that focuses on physical and social aspects of play, we have chosen to shape our contribution by studying the playground, a form of entertainment for children which is incredibly popular in most countries, and which has recently emerged as a target of interest within HCI research. Our approach has been to use data collected during a carefully-structured workshop to develop a set of sensitizing concepts that help explain the specific appeal of the playground as a place where children can take part in playful interaction, but which have the potential to inspire the future design of systems that feature playful interaction. We present these concepts in section 5 of this paper, and then illustrate their creative potential in section 6 by discussing their relationship to the design of Breathless, a public event constructed around a novel interactive installation which has been designed by the authors, and which represents a dramatic evolution of the playground swing. Firstly, however, section 2 provides a description of the playground and considers relevant research, and section 3 describes the methodological basis of the work presented in this paper, with a focus on the use of sensitizing concepts to make a contribution to knowledge. Section 4 then provides an overview of the structure and proceedings of the workshop that we organised. After the presentation of sensitizing concepts, we then discuss knowledge that has been gained in relationship to them through an analysis of data collected during Breathless. Finally, the paper concludes with more general reflections inspired by these concepts, and with a brief discussion of the topic of future research structured around them.

The playground

The playground is a term that has a variety of meanings across different cultures. For the purposes of this paper, we have constrained the scope of our research by only considering playgrounds that have been designed for children and which are situated outdoors. This differentiates the playground from the park, a space reserved for the leisure of the wider population [START_REF] Jones | The invention of the park: from the Garden of Eden to Disney"s Magic Kingdom[END_REF], and from the trend to provide playgrounds that are targeted at adults [START_REF]Internet article on adult playgrounds[END_REF]. Of course, playgrounds may be situated in parks, and adults may have a role in the activities that take place in them, but our focus is on spaces that have been designed with the needs of children in mind. Our rationale is that the design of such spaces has a long and well-documented history, especially in relation to playgrounds intended for urban spaces [START_REF] Solomon | American playgrounds: Revitalizing community spaces[END_REF], and, in the UK at least1 , the provision of playgrounds for children has been taken as a shared responsibility of local and national government. This means that there is currently an active community of professionals with a substantial expertise in playground design, as evidenced by the existence of companies that design and construct playgrounds [START_REF]Playground designers[END_REF]. The playground is also a current topic of research within a variety of academic disciplines, including child development [START_REF] Ladd | Predicting preschoolers" peer status from their playground behaviors[END_REF] and educational psychology [START_REF] Barbour | The impact of playground design on the play behaviors of children with different levels of physical competence[END_REF]. Given this level of external expertise, the challenge for the authors has been to design a research process that focuses on enabling the integration of prior expertise into HCI research, rather than focusing on a process that generates new knowledge in its own right. Section 3 of this paper describes the methods that we have chosen for this task, and the remainder of this paper considers the results that have been produced by it.

The design of playgrounds for children is also an active area of HCI research, much of which focuses on augmenting playgrounds with interactive features. Much of this research has been constructed around an explicit manifesto of encouraging physical exercise and social interaction, motivated by the need to reduce childhood obesity and to increase social contact (for example, [START_REF] Sturm | Key issues for the successful design of an intelligent interactive playground[END_REF]). However, there are also examples of interactive playground equipment that have just been designed to provide interesting new affordances for play [START_REF] Seitnger | A new playground experience: going digital?[END_REF], rather than changing lifestyles. Within this research effort, Sturm et al [START_REF] Sturm | Key issues for the successful design of an intelligent interactive playground[END_REF] have classified potential interventions, using two different set of dimensions. The first relates to the type of intervention that can be made; categories include installations of interactive technologies (such as interactive water games [START_REF] Pares | Massive flux design for an interactive water installation: WATER GAMES[END_REF]), interactive props (such as the LEDball [START_REF] Sturm | Key issues for the successful design of an intelligent interactive playground[END_REF], an object that lights up in various colours when shaken or rotated), and interactive surfaces (such as the ADA floor [START_REF] Delbruck | A tactile luminous floor for an interactive autonomous space[END_REF], which can sense people, and respond with different colours of light). A second set of dimensions relates to key design challenges, namely: social interaction, simplicity, challenge, providing goals and feedback. Using the terminology of these two frameworks, the workshop described in the next section primarily focuses on playground interactions that are orientated around installations, rather than props or surfaces. The deliverables of this workshop are set of sensitizing concepts that suggest approaches to design, and which might therefore be considered complimentary to the design challenges set out by Sturm et al, though they are intended to be more widely applicable than just the playground.

Other examples of HCI or design research in the playground mostly relate to specific interventions that have been made. For example, the Interactive Slide [START_REF] Soler-Adillon | Interactive slde: An interactive playground to promote physical activity and socialization of children[END_REF] is a large, inflatable slide, intended for use by multiple children, with an interactive surface created using a projector and a video camera, whilst the Interactive Pathway [START_REF] Seitnger | A new playground experience: going digital?[END_REF] consists of a weight-sensitive pathway which children can stand on, causing various playful actions to occur. An example of an interactive prop is provided by Misund et al [START_REF] Misund | Chase and catch -simple as that? Oldfashioned fun of traditional playground games revitalized with location-aware mobile phones[END_REF], who describe an augmented version of a traditional "chase and catch" game. Derakhshan et al [START_REF] Derakhshan | Adapting playgrounds for children"s play using ambient playware[END_REF] describe the use of artificial neural networks to categorise the behaviour of children who are playing on an interactive surface.

Research methods

As noted previously in this paper, a substantial body of academic expertise in relation to the playground already exists. Therefore, in attempting to understand the appeal of the playground, and to generate knowledge that can inform the future development of playful interactive systems, our approach has been to focus on synthesizing and presenting existing knowledge, through the medium of a focused workshop. This was attended by experts from a variety of backgrounds, and its primary purpose has been an examination of the playground from a number of perspectives. The proceedings and structure of this workshop are described in section 4 below.

Material gathered during this workshop has since been analysed by the authors. Informed by a rich tradition of qualitative research, these analyses have been structured to generate a set of sensitizing concepts, which are presented in section 5. Sensitizing concepts are analytical constructs that "give the user a general sense of reference" [START_REF] Blumer | What is wrong with social theory?[END_REF] and which can guide attention to particular events or behaviours [START_REF] Holloway | Basic concepts for qualitative research[END_REF]. They are a tool that is commonly used in areas of research that require the understanding of people and their interactions, including anthropology, sociology and health-care [START_REF] Bowen | Grounded theory and sensitizing concepts[END_REF]. They are also a tool with a long history of use within research that has impacted on HCI. An example is provided by Crabtree et al [START_REF] Crabtree | Finding a place for Ubicomp in the home[END_REF], who present a set of sensitizing concepts which identify classes of location in the home that are amenable to computation interventions. Such concepts have then inspired the design of systems such as the Drift Table [START_REF] Gaver | The drift table: designing for ludic engagement[END_REF] and LINC [START_REF] Neustaedter | LINC-ing" the family: the participatory design of an inkable family calendar[END_REF], an electronic family calendar. Sensitizing concepts presented in this paper are intended to explain the success of rides in the playground, in order to inspire future playful systems.

Having presented a set of sensitizing concepts, section 6 illustrates their creative application by considering Breathless, a novel installation which represents a dramatic evolution of a playground swing, and which was constructed by the authors. The design and construction of Breathless was led by a professional designer, who drew on the sensitizing concepts presented in section 5 for inspiration, and who integrated a variety of other source materials. Breathless was experienced by more than 50 participants, and a variety of documentary material was gathered in relation to their experience and the running of the event. An analysis of this material is presented in section 6, where it contributes practical knowledge in relation to the sensitizing concepts outlined in section 5.

As stated in section 2, the focus of our workshop was on understanding the appeal of the static installations that are commonly found in playgrounds. In the UK, these tend to include swings, roundabouts, slides, zip-wires and see-saws. Since playground equipment may vary around the world, representative images of these are shown in figure 1. To ensure that any outputs of this workshop were useful to the research community, we were careful to select a group of participants with relevant professional or academic expertise. These included:  a professional playground designer from Free Play, a company that focuses on the integration of research into playground design practice [START_REF]Free Play[END_REF]  members of the Learning Sciences Research Institute [29] at the University of Nottingham who had previously conducted research orientated around play  an experienced ethnographer who had conducted a study of playful interaction  individuals with relevant expertise in interaction design  individuals with relevant expertise in HCI  individuals with relevant expertise in psychology

The workshop was led by a design consultant from Aerial, a company specialising in the design and construction of thrilling experiences [30]. It lasted for a day, and was divided into three sessions, each of which involved work that took place in small groups. Each session began with a short talk by an invited expert, and then involved time to work on a task that was set by the workshop leader. Tasks were designed to draw on the knowledge and experience of participants, both as professionals or academics, but also as adults with personal experience of playgrounds, either as children themselves, or as the parents of children. Tasks were designed to produce tangible outputs, to aid the analysis processes that were planned at the conclusion of the workshop. Tasks were also designed to require both analytical and creative though processes, with the intention of inspiring participants to think about the playground in a variety of different ways, aiming to produce a level of analysis that was suitably deep to make a useful contribution to HCI. The proceedings of each task were recorded in a variety of ways by the authors of this paper, and have since been analysed. The following sessions and tasks took place in this workshop:

Session one

This session began with a talk by a professional playground designer, who described designs that he had produced, and participatory design methods that he had adopted. Participants of the workshop were then split into groups, and each was allocated two of the pieces of equipment that are featured in figure 1 below. For each, participants were provided with a sheet of representative images as a stimulus, and were asked to draw on their personal and professional experience to produce a description of the appeal of each ride. During this session, participants assembled a number of large paper sheets to which post-it notes had been attached, which were then collected by the workshop organisers. Participants also presented their thoughts to the group. Video-cameras were used to capture these presentations for later analysis.

Session two

Different groups were formed for this session, and each was assigned a single type of ride to think about, from the selection shown in figure 1. Participants were then asked to design a novel ride inspired by this, using only mechanical technologies. Participants were provided with sheets of paper to sketch their designs on, which were later collected by workshop organisers. Participants were also asked to present their ideas to the whole group, and these were again captured on video.

Session three

Given the authors previous work on playful technologies which sensed the responses of participants (see section 1), this session began with a talk by an expert, who described a broad range of available sensing technologies, and motivated their use. Participants were then reformed into different groups, and each was given a single type of ride to work on. Participants were then asked to design a novel ride which was inspired by this, but which integrated electronic sensing technologies in some form. For this activity, participants were explicitly told that they could think beyond the boundaries of the playground, and were provided with a selection of materials to construct models of their designs from. As before, group presentations were videorecorded, and photographs of all models constructed by participants were taken. Participants were then given the opportunity to talk about any thoughts that they had in relation to the workshop, which concluded after this session.

Sensitizing concepts

After the workshop, the authors discussed the meaning of the data that had been collected, focusing on trying to understand how our participants thought about the playground. A thematic analysis [START_REF] Boyatzis | Transforming qualitative information: thematic analysis and code development (1 st edition)[END_REF] then led to the sensitizing concepts presented in this section. These have been selected to provide a novel perspective on play in the playground, and for their potential to inspire the future design of playful systems. Each is accompanied by a description drawn from material generated by the workshop, which is intended to support its comprehension by the reader.

Danger and fear are important playground experiences

Many of our participants spoke of exhilarating playground experiences that involved them performing dangerous activities, or being scared of the situations they had got themselves into. Participants talked about using swings as launchers, allowing them to fly through the air and land on the ground, sometimes causing themselves injury, but more normally just enjoying the thrill and pleasure of using their bodies to provide such momentary experiences. Participants also talked about spinning too quickly on roundabouts, worrying about flying off, but being exhilarated by the physical challenge of hanging on despite centrifugal forces. The professional playground designer who introduced the first session talked about expensive playgrounds which had been "KFCed" -Kitted, Fitted and Carpetted for safety -and which were almost always underused because of this. Participants also talked about the social fears that could be created by interactions between the different age groups that might use a playground, but focused on the importance of such situations for learning how to interact in a social environment. In particular, playing with the older children on a ride for the first time was seen as a scary but important social barrier to overcome by some participants, and an important part of the process of growing up.

Loss of control is a key component of playground installations

Our participants considered that some of the exhilaration described in relation to the previous concept is provided by the loss of control that is inherent in many rides. This is obvious on an installation such as a zip wire, where, after launching, the rider allows themselves to be controlled by gravity, potentially leading to an exciting ride experience whose duration can barely be influenced. Loss of control can be part of the experience of taking part in a swing, since a rider can be pushed higher and higher by someone standing on the ground, allowing them the thrill of exceeding their own comfort zone in a way which they may not be able to manage on their own. The sharing of control is a key part of the experience of a see-saw, in which control oscillates in a rhythmic way between the two participants, both of whom have some control over, and some responsibility for, the others safety during this cycle. Participants also considered loss of control to be an important part of the roundabout experience, as a rider who had boarded a roundabout could then be spun faster and faster by those standing on the ground, causing them to have to hang, fall off or take the risk of jumping off and potentially injuring themselves.

Play often involves the re-appropriation of installations in unexpected ways

Participants talked about re-appropriation as a key issue, and described examples of it leading to enjoyable forms of play. Participants talked about the fun of using a swing in ways for which it was not designed, either by trying to swing left and right (rather than forwards or backwards), by trying to balance on it in unusual ways, by getting several people to ride the swing at once, or by using it as a launcher. One participant described a game in which he lay on the ground underneath a swing seat, which was then thrown towards his head. The chains attached to the seat would restrain it, but the play of the game involved flinching as little as possible as it was thrown. There were many other examples of appropriation that were given during the workshop, including the re-appropriation of equipment by older groups of children for "social loafing", therefore allowing them to exert control over access to it by younger children. A form of re-appropriation that was emphasised by the professional playground designers was that of fantasy -i.e. children using their imagination to think of the playground in different ways, such as a magical forest. Interestingly, the slide as a piece of playground equipment was criticised by a number of participants as having little potential for re-appropriation, although children could still climb backwards up it.

Installations that cater to different levels of skill can support long-term play

Many playgrounds are used by children with very different ages, and different (and often rapidly developing) levels of physical ability. Playgrounds, although simple, often maintain their level of interest across many years of a child"s life, and our participants considered this to be a beneficial product of the very different levels of skill that could be used on a variety of items of equipment in a playground. For example, a very young child might just enjoy sitting in a swing, under the control of a parent, whilst an older child might enjoy learning to control the movements of their body, in order to swing higher than before. A very developed child might then enjoy the physical challenge of standing on a moving swing. Pushing others on swings is also a playful activity that children of many ages and levels of ability could engage in. As well as being playful and fun, such interactions with playgrounds have the potential to assist the learning of new motor skills, with positive benefits for the development of children. Many of the re-appropriations of playground equipment that participants considered also involved a high level of skill for mastery, and developing a new skill was seen as part of the fun of taking part in these activities.

Different designs of rides offer very different throughputs

Playgrounds are rarely managed environments, and the throughput inherent to particular rides has an impact on the experience of using them. For example, a slide has a fairly clear trajectory [START_REF] Benford | Temporal trajectories in shared interactive narratives[END_REF] in which a participant starts at the top and slides down, unless it is re-appropriated by children who wish to climb back up. Such a trajectory is likely to maintain a high throughput, as the duration of each experience is limited by the length of the slide. In contrast, a roundabout or swing can be used in an open-ended way, and participants may only get off when tired. Such open-ended trajectories may allow participants to experiment with their experience in a playful way, but may cause frustration for other children who are denied access to a quickly moving roundabout or an occupied swing for a long period of time.

Spectatorship and performance are an important part of the experience of play

Many discussions of playground equipment focused on the rider, but spectatorship was also seen as an important role in play, albeit often a transitory one. For example, a child who was trying to push themselves higher and higher on a swing might gain even more enjoyment and motivation if being watched by a peer or a parent, and a spectator who was a child might be inspired to gain a new skill by watching others in the playground performing on rides. Spectatorship is also part of the social interaction in a playground, and there could be some tension between a child who is controlling a piece of equipment, and who wants to carry on using it, and a child who is watching the ride and wanting to use it. Equally, the control of a ride by a social group could be seen as a visible display of power, with understanding how to subvert such power on the part of a spectator being an important social lesson.

Table 1 Summary of sensitizing concepts from the playground, with key elements highlighted in first column

Danger and fear

The excitement provided by a level of danger and fear is important to the success of playgrounds.

Control

Losing control and being pushed past your comfort level is a key component of some playground installations.

Re-appropriation

As part of imaginary and exploratory play, installations are often re-appropriated for purposes that they were not designed for.

Skill

Catering for different levels of skill and development is important for supporting long-term play.

Throughput

Different designs of rides offer very different throughputs, which affects the social use of these rides.

Spectatorship and performance

Watching others on rides, and demonstrating or showing off when on the ride are important parts of playground interaction.

6 Knowledge gained through study of a novel system Section 5 has described a set of sensitizing concepts developed from a workshop themed around the playground, which are intended to provide inspiration for the design of systems that promote physical and social interaction. In keeping with the traditions of this method, we would expect these concepts to be modified, challenged or re-appropriated by ourselves and others as they are integrated into future work. As part of this process, this paper now presents an account of our initial work in applying them, as part of a process which led to Breathless, an installation which was assembled in the autumn of 2010, and which was publicly deployed on a single evening. We begin this section with a description of Breathless, and then present an analysis of material collected during its deployment, which is used to highlight the relationship between this installation and the set of concepts presented in section 5. This paper then concludes with a broader discussion of the practical knowledge that has been gained in applying these concepts, and by considering future work in relation to the development of our sensitizing concepts.

Overview of Breathless

Breathless is an experience constructed around a very large rope swing, which is driven by a powerful electric wheelchair motor controlled by a computer. Figure 2 illustrates the use of this motor to drive a horizontal rope, which in turn transfers energy directly into the rope swing, and therefore affects its movements. For its first deployment, the swing was suspended from the covered roof of an outdoor exhibition space. The horizontal rope made use of two pulleys attached to pillars.

In keeping with the Broncomatic [START_REF] Marshall | Breath control of amusement rides[END_REF] which was described in the introduction to this paper, in Breathless, the movement of the horizontal rope is influenced by the breathing of the rider. In particular, breathing in causes the rope to move one way, and breathing out causes it to move the other way. As such, breathing in synchronization with the natural oscillations of the swing causes it to go higher, whilst breathing out of synchronisation caused it to judder and go lower. The length of the vertical rope that connects the swing seat to the loading point in the ceiling of the space is calculated to create a resonant frequency of 5 Hz (i.e. 12 breaths per minute, which is a natural rate of breathing for humans at rest). The idea is to create an experience that responds strongly to breathing that is in harmony with it, but which feels uncomfortable given breathing that is not in harmony.

Breathless uses a modified gas mask to monitor the breathing of participants, through a custom-designed filter which is screwed into a port in the mask. An image of a participant wearing one of the masks is shown on the left of figure 3. This features a participant who is lying in a custom-made cradle which replaces the seat or knot more commonly found at the bottom of a rope swing. This is designed to make it difficult for a participant to transfer energy into the swing through movements of their body, ensuring that the swing is controlled through the breathing of participants alone. In addition to the unique form of interaction provided by the mechanism described above, the experience of taking part in Breathless is heightened by the structure and theming of the event, which together create an intense experience with a strong sense of immersion, but which still allowed for playful interaction between participants. To accentuate the atmosphere of the experience, the event took place after dark. We also used a wireless microphone attached into the gas mask to collect the sound of participants breathing, and used a powerful amplifier to fill the event space with this sound.

A final element of the event relates to the sensitizing concept loss of control which emerged from the workshop described above. Rather than just allowing participants to control their own experience on the ride, every participant in Breathless actually moves through three different pre-defined roles, allowing them to experience different aspects of control. In general, movement through Breathless is tightly choreographed by event staff, and works as follows:

1. Participants join a queue take part, and arrive at a desk, where they are fitted with an appropriately-sized gas mask, fitted with a breathing sensor, which has been sterilised if previously used 2. This breathing sensor is then activated, and a visualisation of the participant"s breathing appears on a very large projection screen which is visible to all event attendees. This projection screen integrates visualisations of live breathing data being collected from all participants currently wearing gas masks 3. The participant is escorted to a position from which they can observe the operation of the ride (which at this point is being controlled by other participants) 4. The participant is then assisted to mount the cradle, and their movements are controlled for a while by the participant who has just vacated it (and who is now sitting in a chair next to it, as shown in the photograph on the right of figure 3) 5. At some point, control is then switched to the participant who is in the cradle, whose breathing then influences their own movements on the ride for a while. 6. Finally, the participant in the cradle dismounts, and takes the now-vacant position in this seat to control the next rider.

Collection and analysis of material during Breathless

Breathless was designed and constructed over a two-week period, and opened to the public on a single evening, where it was experienced by over 50 participants. Throughout the process of conducting Breathless, we collected a variety of material for later analysis. These included semi-structured interviews with twenty-four participants, ambient video recorded from a number of viewpoints within the exhibition space, and regular interviews with designers during the two-week design process. Much of this material has since been transcribed and analyzed. We now present a number of elements of this analysis, structured by the sensitizing concepts introduced in section 5. This interview material has provided insights that will guide the future of development of Breathless, and other similar experiences. We return to it in the final section of this paper, where we discuss wider issues inherent in designing novel playful systems.

Danger and fear

A number of elements in Breathless were selected for their potential to create fearful, intense experiences, but with no real threat of danger to our participants. For example, our use of gas masks seemed to create the potential for uncomfortable feelings of claustrophobia, and we wondered whether the height that the swing seat could rise to might be emotionally uncomfortable for riders, especially given the amount of momentum which is inherent in the system. We asked participants about these issues in our interviews, and have since collated responses.

Although some participants were clearly made uncomfortable by wearing a gas mask, an analysis of responses suggests that there are actually very subtle differences in perception and past experience between participants that influenced their experience, raising an interesting issue of how to design around the concept of danger and fear in the future. For example, one participant had very poor eye-sight, and had to remove his glasses to put the gas mask on -he then described the resultant hazy view that he had from the swing as being "nerve-wracking", but enjoyable because of this intensity. In contrast, a number of participants who were experienced scuba divers described how wearing the gas mask actually felt enjoyable, because it reminded them of diving. However, one participant, who had been diving once and who had hated it, described how the gas mask reminded her of this unpleasant experience. In terms of the height that the swing reached, most participants stated that this was not sufficient to scare them, and that they would have liked it to have gone higher. However, one participant reported being so scared of how high that he was going that he felt like holding his breath, to make sure that it did not go any higher. Finally, although many participants reported feeling claustrophobic when they first put the mask on, a number described how, once they relaxed into this experience, they actually started enjoying the experience of wearing it. In relation to this, one participant described how the mask made her feel like she was in a space of her own, whilst another participant described the experience as like being alone in a bubble, and implying that this was an interesting and comfortable situation to be in.

Control

Clearly control is a key part of the experience of Breathless, with participants being in control when they first mount the swing, then losing control at some point in the experience, and then being given the chance to exert control over another participant after they have vacated it. One participant described this final phase as being "powerful", especially given that the participant he was controlling was his friend. Another participant described Breathless as a very playful experience, because of the option of either "making the other person more thrilled by their experience" or "teasing them to experience something a bit more". Most people described wanting to give other participants a nice ride, although one participant described wanting to create "really rough high frequencies and fluctuations so the person would hopefully be a bit more freaked out". One participant described trying to be really careful when controlling the ride of a participant who appeared scared, whilst other participants described the added interest of trying to control someone that they already had a relationship with, such as friends, brothers or sisters. When being controlled by others, one participant reported a bad experience, given by a person who "didn"t really cope with the concept … it was more like "bump, bump, bump", it was more like a wobbly chair". However, others described really pleasant experiences: "it was good, because he really had the knack of it, like he was doing it really smoothly". Interestingly, some participants tried to communicate with the person who was controlling them, but found this difficult, because the gas mask restricted communication. In addition, because control of the swing is somewhat indirect, a number of participants reported never fully feelings sure about when control shifted from the person sitting on the chair to them, though this lack of certainty seems to have been interesting in its own right.

Re-appropriation

Participants were only given a few minutes in each of the three roles in Breathless, giving little time for the kinds of re-appropriation described in section 5. However, interview comments by certain participants have helped us to think about reappropriation in more depth; in particular a number of interviewees described not being able to work out what the purpose of the Breathless setup was, and therefore having to experiment for a while before working out how to use it (and enjoying this experimental part of the experience). These comments remind us of work on ambiguity in design (for example, [START_REF] Gaver | Ambiguity as a resource for design[END_REF]). We wonder whether designs that are more ambiguous are more amenable to re-appropriation -or, alternatively, whether the reappropriation of designs that have an apparently clear purpose is more enjoyable.

Skill

From our own experimentation, we expected participants to take some time to learn how to control the swing in Breathless, and interview material provides some detail about the challenge of this process. An analysis of this material suggests that some participants sometimes drew on previous experience to learn how to control the swing, alongside experimentation with their breathing and its effects on the system. For example, one participant described how martial arts training had led him to consider the ration between his in-breath and his out-breath, which led him to experiment with varying this ratio whilst riding the swing. Other participants described experimenting with the smoothness of their breathing, with the point in the swing-cycle that they breathed at, and with breathing with either their mouth or their nose. One participant stated that he had a bad cold, and described how this made it hard to control the ride. Other participants described having a lack of an intrinsic ability to keep a rhythm, and suggested that this made it harder to get the swing moving higher. Finally, some participants reported that it was much easier to judge the movement of the swing when they were sitting beside it, controlling someone else. In comparison, when riding the swing, they had little vision, so had to try and sense the position of their bodies, by paying attention to the weight that they were putting on the swing-seat, their sense of balance and the visceral feelings of acceleration that were induced in their stomach.

Throughput

For the designers of Breathless, throughput was a key issue when preparing for the public event. A large number of participants were expected, and there was no clear incentive for riders to dismount the swing, and to give way to others. The movement of participants through three roles was a clear response to this issue, and movement between these roles was created in a variety of ways. Primarily, event staff were in charge of the electronic linkage between breathing sensor and ride movement, and could disconnect this when a participant had experienced a reasonable amount of time on the swing. Other event staff were then on hand to move participants through the positions that related to roles. Such a high level of choreography contrasts strongly with the situation in a typical playground, in which throughput is managed through social interaction; clearly, therefore, although choreography is one tactic for maintaining throughput, other tactics may be worth exploring.

Spectatorship

A number of participants reported how the experience of spectating Breathless influenced their experience of taking part. For example, one participant reported watching the visualization of her breathing that was displayed on the projection screen, and learning how the trace responded to in-breaths and out-breaths. Another described being made to feel nervous by the spectacle of a person in a gas mask, swinging backwards and forwards in the dark. One participant noticed that her breathing appeared very different to other participants, and practiced making it more similar -which then helped her on the ride. Finally, another participant reported swearing by mistake, and then realizing that this had been heard by the whole of the audience -which therefore made her feel self-conscious.

Discussion -lessons learned, and future work

In this paper, we have presented a set of sensitizing concepts derived from an analysis of the playground, and illustrated their creative application to Breathless, an installation which represents a dramatic evolution of the playground swing. In this section, we now present some brief reflections on the knowledge that has been gained through this process, structured through two core themes -accounting for individuality and considering trade-offs between concepts. We also provide a commentary considering the relationship between inclusive design and playful interaction.

Accounting for individuality

A key observation in relation to the research material gathered through Breathless is the impact of participant history and personality on the nature of their experience in this event. To give two examples: participants who had previously had pleasurable experiences whilst scuba diving seemed more likely to enjoy the isolating feeling of wearing the gas-mask during the event, and participants who had worn gas-masks at school (possibly through drills designed to practice response to chemical attacks) seemed more likely to at least be comfortable with wearing the mask. There also seemed to be some differences between participants in relation to their perceptions of the height that the swing rose to, with some participants being scared by this, but with other participants wanting a more extreme experience than we could provide. Collectively, these observations hint at the challenge of designing playful experiences that are enjoyable and beneficial to those that take part in them. In relation to these observations, two opposing tactics suggest themselves: Aim for universality: This tactic, which may be closest to traditional playground design, is to aim for experiences that are as universal as possible. The concepts presented above provide a resource for working within this tactic, but it must present a significant challenge due to the nature of individuality. Universal designs might be relatively generic (like most playground equipment). Designers might also consider approaches such as focusing on installations that can be dynamically adapted to the personality and abilities of their users, to maximize the range of individuals for whom they are relevant.

Design for specific groups: Abandoning universality allows the freedom to design for specific groups of individuals. In relation to Breathless, for example, we could imagine a variant that provided a far more thrilling experience for those who would appreciate it (i.e. an approach which emphasizes danger and fear), or a second variant that was more focused on supporting re-appropriation. This tactic raises an issue of how to identify groups that are interesting to design playful systems for. It also raises issues such as how to profile participants and allocate them to groups.

Considering trade-offs between concepts

A second issue that is highlighted by material collected during Breathless is the potential trade-offs that might have to be made when using the concepts presented in this paper as a resource for design. In Breathless, for example, a clear trade-off had to be made between allowing participants sufficient time on the swing to start to think about re-appropriation and maintaining a sufficient throughput to give all attendees at the event a chance of getting involved. This relates to the nature of the event, which only ran for one evening, and which presented a novel experience which many attendees wished to sample. Playgrounds negotiate this trade-off differently -by often being continuously accessible (and therefore reducing contention) and by relying upon human interaction to resolve contention. Equally, however, contention in the playground can lead to some users being denied access to equipment.

Other trade-offs undoubtedly exist between these concepts, and exploring them seems to be an interesting direction for research. When a trade-off has to be made, it may be that investigations into the available tactics within that trade-off could provide benefits.

Inclusive design in relation to playful systems

Finally, we wanted to acknowledge the potential importance of inclusive design and playful systems, in relation to the concepts that we have outlined above, and especially in relation to play that encourages physical and social interaction. In particular, we wanted to highlight issues around the concept of danger and fear. Even in today"s risk averse societies, playgrounds still offer an opportunity for the ablebodied to experience the pleasures of flirting with danger, albeit with some safeguards to help avoid injury, such as play surfaces to fall onto that are soft in comparison to older materials such as concrete or gravel. However, a number of authors have argued that, when seeking to design for individuals with disabilities, there is often an excessive emphasis on safety, which carries a risk of denying worthwhile experiences around danger and fear to these individuals [START_REF]Inclusive design case studies[END_REF]. When seeking to design within the set of concepts presented in this paper, there is therefore an interesting challenge of how to ensure that as wide a group of individuals as possible are given the opportunity of gaining benefit from playful systems that embed these concepts. In particular, we might pose the question of how to design playful systems that are amenable to interaction for individuals with disabilities, but which still allow for creative re-appropriation, and which still allow for controlled elements of danger, for those participants that wish to take risks.

Playgrounds provide a relatively universal experience which involves physical and social interaction, and which encourage play. Our analysis of a workshop focused on the playground has provided significant inspiration for the design of Breathless, a novel interactive experience, and we hope that it will provide inspiration for others. We can imagine future work that involves novel design, and which draws on these concepts. We can also imagine future work that uses them as an analytical framework when considering existing design.

Figure 1

 1 Figure 1 Play equipment commonly found in UK playgrounds. (Clockwise from top left) Swings, slide, zip-wire, roundabout, see-saw.

Figure 2

 2 Figure 2 Illustration of mechanism of rope swing

All authors are resident in the UK

Acknowledgments

This work was supported by the Horizon Digital Economy Hub (EP/G065802/1).


Anirudha Joshi
email: anirudha@iitb.ac.in

N L Sarda

Do Teams Achieve Usability Goals? Evaluating Goal Achievement with Usability Goals Setting Tool

Keywords: Usability goals achievement, usability goal parameters, latent goals, design tools, methods

Do teams achieve important usability goals most of the time? Further, is goal achievement uniform or are practitioners more mindful of some goals than others? This paper presents an empirical study on usability goal achievement in industry projects. We used Usability Goal setting Tool (UGT), a recommender system that helps teams set, prioritize, and evaluate usability goals. The practitioner creates profiles for the product and its users. Based on these inputs, UGT helps the practitioner break down high-level usability goals into more specific goal parameters and provides recommendations, examples, and guidelines to assign weights to these parameters. UGT suggests strategies to evaluate goal parameters after the design is ready and assign them scores. UGT was used to collect data from 65 projects in the Indian software industry in which participants assigned weights and scores to the goal parameters. The 30 goal parameters suggested by UGT were found to be internally reliable, and having acceptable granularity and coverage. It was observed that goal parameter weights and scores correlated, but only moderately. Another interesting observation was that more than a third of the important goal parameters did not score well. We identify eight goal parameters that are typically high-weighted but have poor weight-score correlations. We call these "latent but important" goal parameters. Design teams will do well to pay closer attention to these goal parameters during projects.

Introduction

Setting goals is an important step early in the design process. Setting goals before design gives the team a target to achieve. Goals help guide the design process, make the design activity tangible, and help evaluate the designs. In the field of humancomputer interaction (HCI), often multi-disciplinary teams are involved; hence, setting goals early and getting an agreement from all stakeholders is important.

Goal have been discussed extensively in HCI literature [START_REF] Nielsen | Usability Engineering[END_REF][START_REF]1997 Ergonomic Requirements for Office Work with Visual Display Terminals[END_REF][START_REF] Mayhew | Usability Engineering Lifecycle[END_REF][4][START_REF] Preece | Interaction Design, Beyond Human-Computer Interaction[END_REF][START_REF] Cooper | About Face 2.0[END_REF][START_REF] Shneiderman | Designing the User Interface: Strategies for Effective Human-Computer Interaction (4th Edition)[END_REF][START_REF] Bevan | Classifying and Selecting UX and Usability Measures[END_REF][START_REF] Hornbaek | Making Use of Business Goals in Usability Evaluation: An Experiment with Novice Evaluators[END_REF]. To help teams set goals, we developed a Usability Goal Setting Tool (UGT) [START_REF] Joshi | Usability Goals Setting Tool[END_REF], [START_REF] Joshi | Usability Goals Setting Tool -Online Version[END_REF]. UGT maintains a repository of profiles of past projects, their users, goals, and scores. Based on this experience, UGT provides guidance to HCI practitioners to set and evaluate usability goals in new projects. Is such a tool necessary or is the current knowledge, skills and practices sufficient to let HCI practitioners set usability goals and evaluate products against them? During our interactions with software development teams in the industry, we observed that HCI practitioners are often unclear about the usability goals of the product they are designing. In some cases, the HCI practitioners are clear, but there is no explicit agreement on these by the other stakeholders in the team.

The questions we investigate in this paper are: To what extent do teams achieve their usability goals? Do teams achieve the important usability goals most of the time? Further, is goal achievement uniform or are practitioners more mindful of some usability goals than other?

We collected retrospective data with the help of UGT from projects in the Indian industry to evaluate goal achievement. We explored the data to establish the coverage, relevance, granularity, and internal reliability of the goal parameters.

In section 2, we review literature related to goal setting in design and in HCI literature. Section 3 gives an overview of UGT. In section 4, we present the data collected from industry projects and investigate the coverage, relevance, granularity, and internal validity of goals suggested in UGT. Section 5 investigates the goal achievement in these projects. Section 6 talks about conclusions and future work.

Goals in Design and HCI

The importance of goal-driven design has been stressed in literature for a long time. Design for a 'need' has been a part of traditional industrial design thinking. Charles Eames reportedly said, "Design is a plan for arranging elements in such a way as best to accomplish a particular purpose" [START_REF] Eames | Charles Eames Quotes[END_REF]. Archer explains that since design is necessarily associated with change, identifying goals means "defining the needs and pressures, which constitute the driving force for change". The first step is to determine the goals of the design effort together with "the essential criteria by which a 'good' solution will be distinguished from a 'not so good' solution" [START_REF] Archer | Systematic Method for Designers[END_REF].

The closely related fields of HCI, usability, interaction design, and information architecture emphasise the importance of usability goals. ISO 9241 defines usability as the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use [START_REF]1997 Ergonomic Requirements for Office Work with Visual Display Terminals[END_REF]. Shneiderman and Nielsen agree on five high-level usability attributes of a productlearnability, speed of use, error-free use, retention over time, and subjective satisfaction [START_REF] Shneiderman | Designing the User Interface: Strategies for Effective Human-Computer Interaction (4th Edition)[END_REF], [START_REF] Nielsen | Usability Engineering[END_REF]. Mayhew categorizes usability goals as qualitative and quantitative, and as performance goals, preference goals, and satisfaction goals [START_REF] Mayhew | Usability Engineering Lifecycle[END_REF]. ISO 9126-1 describes usability in terms of understandability, learnability, operability, and attractiveness [4]. Cooper and Reimann emphasise the importance of goals in usability and interaction design process [START_REF] Cooper | About Face 2.0[END_REF]. Hornbaek et al. suggest a technique to integrate business goals in usability evaluations [START_REF] Hornbaek | Making Use of Business Goals in Usability Evaluation: An Experiment with Novice Evaluators[END_REF]. Bevan summarises several other ways of organising usability measures, which could be looked upon as goals [START_REF] Bevan | Classifying and Selecting UX and Usability Measures[END_REF].

One purpose of defining these usability goal-sets was to reduce the ambiguity associated with the terms "usability" or "user-friendliness", and define them in terms of measurable components. Usability has been recognised to be a multi-dimensional property that needs to be broken down into measurable attributes such as learnability, speed of use etc. [START_REF] Nielsen | Usability Engineering[END_REF].

However, these attributes themselves are still at too broad to be interpreted consistently in the context of a given project. For example, one can interpret learnability as "users should take less time to learn to use the product" or as "users should be able to learn to use the product on their own". Error-free use could be either interpreted as "product should not induce errors", "product should tolerate user's errors", or "product should help the user recover from errors". These interpretations could lead to communication gaps between team members and could make it difficult to evaluate the design. As summarised below, our approach in UGT is to split high-level usability goals into more granular, measurable, and less ambiguous goal parameters.

Relatively recent research interest in human emotions has broadened the traditional focus of researchers from usability to user experience. However, approaches to user experience goals are not universal. Unlike in usability, where high-level goals have been more or less agreed upon, when it comes to user experience design, there seems to be much less agreement. After a survey of user experience professionals, Law et al concluded that the concept of user experience is dynamic, context-dependent, and subjective [START_REF] Law | Understanding, Scoping and Defining User eXperience: A Survey Approach[END_REF]. There is no single accepted definition of what user experience is, and some researchers question whether the user experience could be designed at all [START_REF] Mccarthy | Technology as Experience[END_REF].

While there may be no explicit agreement on a list of user experience goals, most practitioners favour a "goal-driven" approach in design of interactive products, e.g. [START_REF] Mayhew | Usability Engineering Lifecycle[END_REF], [START_REF] Preece | Interaction Design, Beyond Human-Computer Interaction[END_REF], [START_REF] Cooper | About Face 2.0[END_REF]. When a practitioner sets goals in a particular project, he may not explicitly differentiate between whether a particular goal is related to usability of the product or its broader user experience.

In a typical industrial context, it may not be possible to meet all goals and it is necessary to prioritize. Depending on the context, users, and platform, some goals may be more important for a project, while others might be irrelevant. The need of prioritising goals has been acknowledged for a while. For example, Archer talks about "rank ordering" sub-problems as a method of prioritizing goals and resolving conflicts [START_REF] Archer | Systematic Method for Designers[END_REF]. More recently, Cross talks about an objective tree method -organizing objectives into a hierarchy of higher and lower level objectives [START_REF] Cross | Engineering Design Methods 3rd[END_REF]. Shneiderman states, "a clever design for one community of users may be inappropriate for another community", and "an efficient design for one class of tasks may be inefficient for another class" [START_REF] Shneiderman | Designing the User Interface: Strategies for Effective Human-Computer Interaction (4th Edition)[END_REF]. However, other than UGT (which we summarise below), there has been no guidance to prioritize usability goals systematically.

In our earlier work, we found that goal achievement is affected by the process. When HCI activities are better integrated with software development, teams following Agile processes achieve their usability goals better than teams following the Waterfall process [START_REF] Joshi | Measuring Effectiveness of HCI Integration in Software Development Processes[END_REF]. We also found that unless they integrate HCI activities with software development rigorously, companies providing software development services do worse in usability goals achievement than companies involved in software product development. Elsewhere, we report the relative contributions of different HCI activities on goal achievement [START_REF] Joshi | Evaluating Relative Contributions of Various HCI Activities to Usability[END_REF].

Despite the extensive literature on usability goals, there have been no empirical studies on the extent of usability goals achievement. We also do not know if some usability goals are achieved more frequently than others are. Further, it is not clear whether the current understanding of goals among practitioners is sufficient, or tools such as the UGT are necessary to improve goal achievement. In this paper, we present one such study.

UGT Overview

The primary purpose of UGT is to help set usability goals, given a context of user goals and business goals [START_REF] Joshi | Usability Goals Setting Tool[END_REF]. This section provides an overview of UGT. A more detailed version of UGT including systematic instructions is available online [START_REF] Joshi | Usability Goals Setting Tool -Online Version[END_REF].

UGT is envisioned as a recommender system (Fig. 1). Based on prior experience of similar product and user profiles, UGT recommends priorities for usability goals. UGT also recommends usability evaluation guidelines. At all times, the practitioner has the freedom to add goals, edit, or re-word the suggested goals, to regroup goals, or to evaluate them differently than suggested in UGT. These decisions are collected and fed back into UGT to improve its recommendations in future, making UGT flexible and extensible.

Goal Parameters in UGT

UGT helps break down high-level usability goals into 30 concrete, specific, and measurable goal parameters (Table 1). These were derived from the usability attributes suggested by Shneiderman [START_REF] Shneiderman | Designing the User Interface: Strategies for Effective Human-Computer Interaction (4th Edition)[END_REF] and Nielsen [START_REF] Nielsen | Usability Engineering[END_REF], and elaborated through brainstorming and formative evaluations as discussed in [START_REF] Joshi | Usability Goals Setting Tool[END_REF]. Our attempt is to keep these goal parameters granular, concrete, and yet relevant to a large number of projects.

The HCI practitioner determines the importance of each goal parameter in the context of his project by assigning it a suitable weight. Weights express the relative importance of goal parameters in the context of a project. For example, a product meant to be used several times a day is likely to have higher weight for a speed related goal parameter such as goal parameter 8, "user must be able to do primary task / frequent tasks quickly, easily, at all times". A one-time use product might give higher weight to learnability and ease of use goal parameters such as 1, "findability: options / data / information should be visible / easy to find" and 17, "intuitiveness: user should be able to predict the next step / task". A life-critical product is likely to rate highly error-free use goal parameters such as 25, "product should not induce errors" and may sacrifice a learnability goal parameter such as 3, "users should be able to learn on their own".

We suggest the following scale for assigning weights: Extremely important / unique selling proposition [START_REF] Preece | Interaction Design, Beyond Human-Computer Interaction[END_REF], very important (4), important (3), usual relevance / hygiene factor (2), somewhat relevant (1), irrelevant (0). Based on experience of prior projects, UGT recommends weights for the goal parameters on this scale [START_REF] Joshi | Usability Goals Setting Tool -Online Version[END_REF].

We do not claim that the goal parameters and weights recommended by UGT cover all aspects of user experience in every situation. They are suggestive of the kind of goals that the practitioner could set. An experienced practitioner may assign different weights, add, edit, or re-word the suggested goal parameters, or group goal parameters differently if preferred. Yet, as we report below, the current list of goal parameters seems to have wide coverage, reasonable relevance, and sufficient granularity.

Goal-setters should be aware that while it may be tempting to set a high weight to each goal parameter, it might not be necessary, practical, or even possible to achieve such a design. The weights should reflect the priorities of the business, the stakeholders, and the users. The weights would help prioritize usability evaluation activity as the highest rated goals and parameters would be evaluated more rigorously.

After the evaluation, practitioners can assign a score to each goal parameter. We suggest the following scale for assigning scores: Outstanding, exceptional, best possible user experience against this goal parameter (100); acceptable, good enough, though not exceptional (75), undecided, neither good nor bad (50), bad, but not the worst (25), very bad, worst possible user experience for this goal parameter (0).

Table 1: Goals and goal parameters in UGT.

Using UGT

The HCI practitioner approaches UGT when he is clear about the product brief and has sufficient understanding about the domain, the problems, the context, and the users. Using UGT involves four steps: initiate, set goals, review goals, and set evaluation guidelines.

To begin with, UGT asks the practitioner to specify the product profile and one or more user profiles. The product profile captures information such as the industry domain, the work-practice domain, the expected cost to the user, the platforms, and the number of user profiles. Each user profile captures further information such as the age, the expected level of tech-savvyness of the user, the frequency of use, the product complexity, and the motivation of the user to use the product.

The product profile and the user profile form the input to UGT. Based on these, UGT provides recommendations for assigning weights to the goal parameters. Detailed recommendations for all the 30 goal parameters are available online [START_REF] Joshi | Usability Goals Setting Tool -Online Version[END_REF]. These recommendations have been derived from experience of projects for which UGT has been used so far.

After the practitioner has done one pass of assigning weights to goal parameters, the list of goal parameters is re-presented, this time sorted by their weights. Goal parameters with weights that deviate substantially from the recommended range are highlighted. The practitioner reviews the weights and tweaks them. This step was introduced because it was observed during evaluations that practitioners overassigned weights in the first pass, but preferred to tone them down during a review.

UGT recommends evaluation guidelines of each goal parameter. It recommends at least one possibility for a user-based test and one for a review-based evaluation. The evaluation guidelines for the 30 goal parameters are available online [START_REF] Joshi | Usability Goals Setting Tool -Online Version[END_REF]. These are based on the formative evaluation reported in [START_REF] Joshi | Usability Goals Setting Tool[END_REF], and further data from projects where UGT has been applied so far.

As shown in Fig. 1, UGT has self-learning capabilities. The practitioner may use UGT recommendations or choose to override them. These decisions are captured and fed back to enrich UGT further. As UGT collects data from more projects, it gives more accurate and relevant recommendations.

Data and Analyses

Using UGT, we collected data about goal parameter weights and scores from industrial projects. First, we evaluate whether UGT goal parameters have sufficient coverage, relevance, and granularity, and whether the weights and scores used in UGT are internally reliable. Next, we determined the extent to which the HCI practitioners achieved goals of their projects, and whether practitioners are likely to be equally mindful of all goals parameters. HCI practitioners from the Indian IT industry were trained on UGT. Then they were invited to participate in the study by contributing data from industry projects that they had recently completed. For each project, following data was collected:

• Product profiles and user profiles • Goal parameter weights (0-5)

• Goal parameter scores (0-100). Participants were encouraged to use information from usability tests, reviews, and user feedback where available while giving their scores. 44 HCI practitioners participated and contributed data from 65 projects. Some participants contributed data from more than one project. The participants came from a wide variety of companies including four large (25,000+ employees) companies engaged in developing software on contract, a few relatively smaller companies, some multi-national companies with large product development centres in India, and smaller product development companies. The projects represented a wide variety as well. These included different platforms (desktop, web and mobiles), industry domains (finance, telecom, entertainment etc.), targeted users (call centre agents, sales persons, farmers etc.), types of business models (contracted software development companies and product companies), and process model used (waterfall and agile).

Table 2 lists the number of projects that assigned a particular weight (from 0 to 5) and a particular score (0-25-50-75-100) to each goal parameter. It also lists the means and standard deviations of weights and scores of each goal parameter.

Goal Parameter Coverage, Relevance, Granularity and Reliability

While recommending goal parameters in UGT, our aim was to achieve a reasonable level of granularity so that the goal parameters are concrete, specific, measurable, and interpreted unambiguously. At the same time, we wanted the goal parameters to be widely applicable, relevant to a large number of projects, and internally reliable. We evaluated the data from projects to verify if this was indeed the case. Coverage is the extent to which the goal parameters suggested by UGT suffice the goal-setting needs of a project. One method of evaluating if UGT has enough coverage was to look at how many new goal parameters were added by practitioners. Throughout the study, the participants had the freedom to add, edit, merge, or regroup goal parameters if the suggested ones did not suit their needs. This was indicated to them at the beginning of the study. To remind the participants, the UGT form always had blank lines under each group of goal parameters and at the bottom as shown in Table 1. After assigning goal weights, the participants were encouraged to express goals relevant to their projects beyond the ones listed in UGT.

A majority of the participants did not specify additional goal parameters. The goal parameters currently recommended in UGT could express goals in 59 out of 65 projects to the satisfaction of the practitioners in those projects. Practitioners of only 6 projects added goal parameters. Among these, 4 specified one additional goal parameter each, and 2 specified 2 additional goal parameters each. We can conclude that currently UGT has a reasonable coverage and is applicable to a majority of projects in the industry.

Relevance is the number of goal parameters that could be removed from UGT without hampering coverage significantly. Table 2 lists the number of projects that assigned a particular weight to each goal parameter. Out of the (65 projects x 30 goal parameters=) 1,950 cases, a weight greater than 0 is assigned to 1,757 (90%) cases and in only 193 (10%) of the 1,950 of the cases, the weight was set to 0 (irrelevant). As we can see in Table 2, weight 0 is not restricted to a few goal parameters, but spread across several. Further, even goal parameters weighted irrelevant by a large number of projects (goal parameter 6 and 15, for instance) have been weighted important (3 or more) by many other projects. We can conclude that the goal parameters suggested in UGT are relevant to projects.

Granularity is the extent to which UGT helps break down high-level goals into concrete goal parameters. Our aim was to achieve a good balance of granularity. We wanted the goal parameters to have sufficient granularity to allow practitioners to express themselves precisely, and yet not so fine that they cannot differentiate between adjacent elements. If the list of suggested goal parameters were too long, it could hamper the usability of UGT itself.

We could consider the granularity of UGT in two ways; the granularity of the goal parameters and the granularity of the scale (weights 0-5).

During the study, the participants seemed comfortable with the scale. Assigning a specific meaning to each point on the scale seems to have helped. Once they got used to it, the participants could easily differentiate between the adjacent points on the scale and could justify why one goal parameter would have a weight of 2 while another would have a weight of 3.

Granularity of the goal parameters is harder to evaluate. In some cases, a few of the goal parameters could be split up further and made more granular, e.g. goal parameter 29 "user should feel emotionally engaged / brand / fun / reflective appeal / trust". On the other hand, since none of the participants felt the need for doing so for their projects though they had a choice, it is perhaps not necessary.

Our objective behind splitting high-level goals into goal parameters is to make goal setting less ambiguous and consistently interpretable. During the study, participants could interpret the goal parameters unambiguously. Occasionally, they needed to refer to the UGT documentation and go through examples for some of the goal parameters. Nevertheless, once they understood the meaning, they could unambiguously interpret the goal parameter in the context of their project, determine its importance, and think of ways to evaluate that goal parameter. We believe that we have achieved a right balance of granularity in UGT goal parameters. Of course, in case a particular project needs more granular goal parameters, UGT always allows for the flexibility.

When variables are used as components of a larger construct, their internal consistency reliability is important. Internal consistency reliability is the extent to which individual variables are measuring the same underlying construct of interest [START_REF] Hatcher | A Step-by-Step Approach to Using the SAS System for Factor Analysis and Structural Equation Modeling[END_REF]. Cronbach's alpha evaluates the variation accounted for by the true score of the underlying construct. Cronbach's alpha above 0.7 is considered an acceptable measure of internal reliability. To test if any particular component varies differently than the other components, and therefore does not measure the same underlying construct, that component is dropped and alpha is calculated again with remaining components. If the resulting alpha increases substantially, then that component is not measuring the same underlying construct and it must be deleted.

The overall internal reliability of the 30 goal parameters in the 65 projects using Cronbach's alpha was 0.7870 for the weights, and 0.8733 for the scores. Both values indicate an acceptable level of internal reliability. Each of the 30 goal parameters was deleted by turns and Cronbach's alpha was re-calculated for the remaining 29 goal parameters. The resulting alphas did not vary much -from 0.7720 to 0.7969 for weights and from 0.8629 to 0.8780 for scores. The alpha resulting from dropping any particular goal parameter did not increase by much (maximum increase < 0.01). We can conclude that the 30 goal parameters are internally consistent and essential to measure the same construct.

Goal Achievement

We analysed extent to which the HCI practitioners achieve goals of their projects. In an ideal situation, design teams would like to score well against all goal parameters. In practice, if resources were limited, design teams would still like to score well on high-weighted goal parameters. This analysis was done to test the following hypothesis: Design teams naturally concentrate on achieving the high-priority goals; goal weights and goal scores are positively correlated.

This hypothesis can be tested in two different ways. We can evaluate the correlation between the mean weights and mean scores of the 30 goal parameters reported in Table 2. However, mean weights and scores can disguise the divergence between individual weight-score pairs. Therefore, we can also evaluate the correlations between individual weight-score pairs (65 projects x 30 goal parameters = 1,950 pairs).

Pearson's correlation r is used to evaluate correlations between parametric variables, where r 2 indicates the extent of variation in the dependent variable because of the independent variable [START_REF] Kurtz | Introduction to Social Statistics[END_REF]. Pearson's correlation of mean weights and mean scores of the 30 goal parameters (Table 2, n = 30) was calculated. A significant positive and strong correlation resulted (r = 0.957, n = 30, p < 0.0005, r 2 = 0.916). We can conclude that the mean weights of goal parameters strongly correlate with mean scores of goal parameters, and mean weight of goal parameters predicts 91.6% variation in mean scores.

Next, a crosstabs summary was generated for the 1,950 weight-score pairs (Table 3). This shows how many goal parameters achieved each weight-score pair. For example, among the goal parameters that were set a weight of 5, 52 achieved a score of 100, while 97 achieved a score of 75. We can see that out of 1,950 goal parameters 757 (43%) scored 50 or less (undecided or worse). A matter of particular concern is that goal parameters with weights 3, 4 and 5 (the important goal parameters) scored 50 or less in 39%, 36% and 33% cases respectively (the gray cells in Table 3). Spearman's rho is used to evaluate correlations between ordinal variables and the square of the Spearman's rho indicates the extent of variation in the dependent variable because of the independent variable [START_REF] Kurtz | Introduction to Social Statistics[END_REF]. As the goal parameter weights and scores are ordinal variables, a Spearman's rho was calculated between the 1,950 pairs of weights and goal parameter scores reports. A statistically significant correlation emerged but the value of the rho was quite small (rho = 0.391, n = 1,950, p < 0.0005). A correlation value between 0.25 and 0.5 is considered a moderate association. The rho 2 = 0.153. This indicates that only 15.3% of the variation in the goal parameter scores is explained by the variation in the goal parameter weights.

While mean weights and mean scores of goal parameters correlate very well, individual goal parameter weight-score pairs correlate only moderately, and as many as 36.8% of the important goals are not achieved. This could have happened possibly because the practitioners did not set usability goals systematically during the project, or because they did not track goal achievement of important goals explicitly at the end of the project. As a result, they may have not explicitly realised the importance of some of the goal parameters for their projects until they participated in our study.

A limitation of this study was that data was collected retrospectively, i.e. after the projects were completed, and this may have introduced some biases in the data. However, this may not be significantly affecting our main finding that a large proportion of important usability goals are not achieved. It is anecdotally observed that practitioners set more ambitious goals in the beginning of the project than at the end. If at all, it could be possible that in reality an even larger proportion of important usability goals are not achieved.

Latent Goals and Explicit Goals

If the practitioner knew that a goal parameter is important in the context of a project, he would strive to achieve it well. In our study, he would assign that goal parameter a high weight. If he were successful in achieving that goal parameter, he would also assign it a high score.

A high correlation between the weights and scores of a particular goal parameter across projects (Fig. 2a) indicates that largely, practitioners put in efforts to achieve high scores against that goal parameter in projects where it was important. Conversely, a low correlation (Fig. 2b) indicates that scores of that goal parameter are independent of its weights. This could happen if either the goal parameter is either particularly easy or difficult to achieve (and hence uniformly high or low scores), or if the practitioners were not mindful of that goal parameter during projects. If practitioners were equally mindful of all goal parameters during development, there would not be a large variation between weight-score correlations across goal parameters. On the other hand, if some goals tended to be "latent" (i.e. the practitioners were less mindful of them during development), these would tend to have lower weight-score correlations. This analysis was done to test the following hypothesis: Design teams are equally mindful of all goal parameters; weightscore correlations do not vary much across goal parameters.

Spearman's rhos were calculated to explore the relationship between weights and scores for individual goal parameter across the 65 projects. Table 4 lists the rhos and significances for the 30 goal parameters, along with mean weights and mean scores. The statistically significant rhos (p < 0.05) are highlighted in grey. The table has been sorted in the descending order of mean weights assigned to each goal parameter. As reported (Table 2), the mean scores of goal parameters are between 30 and 72 and standard deviations of scores are greater than 16. This indicates that none of the goal parameters was particularly easy or particularly difficult to achieve. Yet, the weight-score rhos are not significant for half the goal parameters (Table 4) in spite of having a reasonable sample size of projects (n = 65). We can conclude that practitioners were not mindful of these goal parameters during projects, but gave them a higher weight during our study.

Interestingly, goal parameters with high mean weights tend to have less significant weight-score rhos (the upper half of Table 4). Conversely, the goal parameters with low mean weights tend to have higher and statistically significant weight-score rhos (the lower half of Table 4). The Pearson's correlation between the goal parameter weight means and the weight-score Spearman's rhos is strongly negative and statistically significant (r = -0.815, n = 30, p < 0.0005).

We can conclude that weights and scores are better correlated for low-weighted goal parameters, but not so well correlated on higher weighted goal parameters. Design teams achieve better scores when a typically low-weighted goal parameter gets an occasional higher weight, but do not achieve similar better scores when a typically high-weighted goal parameter gets an even higher weight.

A possible interpretation is that the typically high-weighted goals are latent but important. These goals are perhaps not explicitly asked for by the stakeholders and hence are perhaps not explicitly evaluated for during usability evaluations. The practitioners gave higher weights to these goal parameters when they saw them listed in UGT during the study, but they were not very mindful of them during the projects.

The following goal parameters have particularly low weight-score Spearman's correlations (rho < 0.15) and are potentially latent but important. Two of these have been plotted in Fig. 3 A corollary to the above would be that low-weighted, high correlation goal parameters are explicit. These are more readily expressed by the stakeholders (such as clients or product managers) and are specifically addressed during usability evaluations. The following goal parameters have high and significant weight-score Spearman's correlations (rho > 0.50, p < 0.05) and are potentially explicit. These 7 goal parameters have a mean weight of 2.21, which is significantly less than the weights of latent goals above (p < 0.0005). Two of these have been plotted in Fig. 4 as an illustration:

Conclusions and Future Work

We knew that there are differences in goal achievement in projects following waterfall and agile process models and between product and services companies [START_REF] Joshi | Measuring Effectiveness of HCI Integration in Software Development Processes[END_REF]. We also knew that some HCI activities contribute to goal achievement more than others [START_REF] Joshi | Evaluating Relative Contributions of Various HCI Activities to Usability[END_REF]. In this paper, we presented an empirical study that looks at goal achievement in 65 industry projects with the help of a tool for usability goal setting (UGT). In these projects, the goal parameter weights and scores correlated, though only moderately. HCI practitioners seem to be achieving important usability goals only moderately better than other usability goals. A particular matter of concern is that more than a third of the important usability goals scored undecided or worse. This clearly establishes the need to pay more attention to explicitly setting usability goals early on in the project, tracking the achievement of these goals during the project, and evaluating against these goals at the end. We also identified the differences in goal achievement patterns between usability goals. Projects seem to score well on a typically less important usability goal when it occasionally becomes more important, but do not achieve better scores when a typically important usability goal becomes even more important. We identified these usability goals that could be interpreted as "important but latent". Practitioners gave a higher weight to these goals when they saw them during the study, but judging by the scores of these goal parameters, we can only conclude that they were not very mindful of these higher weights during the projects.

Further research is needed in goal setting, tracking, and achievement to determine the extent to which goal achievement varies based on variables such as organisational maturity, domain, platform, and experience of practitioners.

The study established the usefulness of a tool such as UGT. In an earlier survey, we had reported that practitioners thought that UGT was useful, it helped them understand the context of the project better, and made them think about goals that they had not considered earlier [START_REF] Joshi | Usability Goals Setting Tool[END_REF]. This study independently corroborates this result. It points to a need for a tool such as UGT that will help practitioners set and track goals during their projects systematically and provides guidance in prioritisation and evaluation of goals. As a long-term activity, organizations can use such a tool to keep a history of past goals, usability evaluations, practices, and costs, and use the repository as a knowledge base for identification and prioritization of usability goals in future projects. More studies will be required to determine if tools such as UGT could help improve usability goal achievement in practice. We also plan to explore the relationships between the user profiles, the product profiles, and the goal parameter weights with the aim of improving the recommendations for the goal parameter weights.

The study had some limitations that we acknowledge. The study comprised of projects from the Indian IT industry only. This could have introduced certain biases. A majority of the projects used the waterfall process model of software development, and a few used agile process models. No projects reported the use of Rational Unified Process models. This proportion may be different in other countries / contexts. The maturity of the usability, the mix of business models (product vs. service) and nature of domains addressed may also be different in other countries. Further, as discussed above, data was collected retrospectively. Thirdly, for most projects, only one representative participated in the study. This happened due to practical constraints. In reality, the data could vary somewhat if we get inputs from multiple stakeholders in each project as UGT is meant to take.

Fig. 1 :

 1 Fig. 1: An overview of UGT usage workflow.

Learnability 1 Findability

 1 : options / data / information should be visible / easy to find 2 User should take less time to learn: (e.g. in < 10 minutes, in < 2 hours practice)[START_REF] Mayhew | Usability Engineering Lifecycle[END_REF] Users should be able to learn on their own 4 Product should be internally consistent 5 Product should be consistent with other products, older methods / past habits 6 Product should be consistent with earlier version 7 User should remember / retain critical, but infrequent tasks Speed of use User must be able to do primary task / frequent tasks quickly, easily, at all times User should be able to navigate quickly and easily Product should not load user's memory / product should not put cognitive load Flexibility: User should control the sequence of tasks User should be able to complete tasks in specific time / no. of steps / in less efforts Product should be personalised for the user automatically Product should be localised for specific market segments User should be able to customise the product for himself Ease of use Interface should clearly communicate the conceptual model Intuitiveness: User should be able to predict the next step / task No entry barrier: user must be able to complete critical first tasks Product should require no unnecessary tasks Product should automate routine tasks / minimise user task load Product should be always on, always accessible Ease of Communication Information architecture: well aggregated, categorised, presented Communication should be clear / user should easily understand text, visuals Error-free use Product should give good feedback / display its current status Product should not induce errors Product should tolerate user's errors / forgiving interface / should prevent errors Product should help user recover from errors / help users troubleshoot problems Subjective Satisfaction User should feel in control of the product / behavioural appeal User should feel emotionally engaged / brand / fun / reflective appeal / trust User should find the product aesthetically appealing / visceral appeal Other goals Add goal parameters specific to your project here.

Fig. 2 :

 2 Fig. 2: Importance / achievement scatter plot for (a) a highly correlated goal parameter, and (b) a non-correlated goal parameter (hypothetical data). Each dot represents data from one project. The pink area represents the projects that gave weight of 3 or more, but scored 50 or less.

Fig. 3 :

 3 Fig. 3: Importance / achievement scatter plot for (a) Goal parameter 23 "communication should be clear", mean weight = 3.89 (SD = 0.89), mean score = 71.54 (SD = 20.19), rho = -0.19 (p = 0.138), and (b) Goal parameter 24 "product should give good feedback", mean weight = 3.55 (SD = 0.97), mean score = 67.69 (SD = 23.27), rho = -0.02 (p = 0.901) (n = 65 in each case). Each dot represents data from one project. The pink area represents the projects that gave weight of 3 or more, but scored 50 or less.

• 6 -Fig. 4 :

 64 Fig. 4: Fig: Importance / achievement scatter plot for (a) Goal parameter 6 "consistent with earlier version", mean weight = 1.32 (SD = 1.75), mean score = 30.38 (SD = 34.09), rho = 0.77 (p = 0.0005), and (b) Goal parameter 13 "product should be personalised for the user", mean weight = 2.23 (SD = 1.70), mean score = 43.08 (SD = 33.80), rho = 0.71 (p = 0.0005), (n = 65 in each case). Each dot represents data from one project. The pink area represents the projects that gave weight of 3 or more, but scored 50 or less.

Table 2 :

 2 Number of projects that assigned a particular weight to a goal parameter, goal parameter weight means and standard deviations, number of projects that assigned a particular score to a goal parameter, and goal parameter score means and standard deviations. # refers to the goal parameter numbers in Table1. (n = 65)

	#	No. of projects out of 65 with		Weights	No. of projects out of with	Scores
				weights							scores
		0	1	2	3	4	5 Mean	SD	0	25	50	100 Mean	SD
	1	0	0	3 13 30 19	4.00	0.83	0	1	16	10 71.92 16.83
	2	1	5 12 24 17	6	3.06	1.13	0	7	22	5 63.08 19.82
	3	5	6 15 14 19	6	2.83	1.40	5	5	16	3 60.38 24.56
	4	1	4 17 19 17	7	3.05	1.16	2	4	18	13 67.69 24.09
	5	5	5 19 18	8 10	2.75	1.41	4	7	31	6 55.38 24.40
	6 37	3	8	6	6	5	1.32	1.75	34	1	14	2 30.38 34.09
	7 10 12 11 17 10	5	2.31	1.52	8	7	26	2 51.15 25.93
	8	3	3	5 14 28 12	3.49	1.28	4	2	10	16 71.15 25.86
	9	1	1 12 11 30 10	3.51	1.11	0	7	11	15 71.15 22.63
	10	1	2 23 14 17	8	3.05	1.18	4	10	15	3 58.08 25.04
	11	7	8 16 19 11	4	2.48	1.37	6	9	22	3 53.85 25.86
	12	4	1 13 20 15 12	3.18	1.33	2	3	22	7 64.62 21.60
	13 15 10 12	6 17	5	2.23	1.70	19	9	12	4 43.08 33.80
	14 17 12	8 10	9	9	2.14	1.79	20	5	18	9 44.62 35.77
	15 29	9	6	8	9	4	1.55	1.73	33	6	9	4 30.38 35.21
	16	0	5	8 18 21 13	3.45	1.17	0	4	20	4 65.77 17.44
	17	1	4 11 25 18	6	3.12	1.10	0	3	27	8 65.38 19.11
	18	7	6 10 19 16	7	2.80	1.47	6	8	20	6 56.54 27.34
	19	3	2 19 26 12	3	2.78	1.08	1	9	16	7 63.46 23.00
	20 10	7 12 16 16	4	2.51	1.51	9	8	22	3 51.15 27.75
	21 10	6 16 10 10 13	2.66	1.70	13	6	11	9 54.62 33.92
	22	0	1	3 24 18 19	3.78	0.98	0	3	15	13 71.92 19.52
	23	0	0	5 14 29 17	3.89	0.89	0	3	17	14 71.54 20.19
	24	0	0 10 21 22 12	3.55	0.97	1	5	19	13 67.69 23.27
	25	3	0 17 24 14	7	3.03	1.16	3	6	22	4 60.00 22.88
	26	3	6 20 24 10	2	2.58	1.10	4	7	28	6 56.54 24.72
	27	2	5 19 18 16	5	2.86	1.20	3	7	24	7 59.62 24.48

Table 3 :

 3 SPSS crosstabs output for 30 goal parameter weights and scores for 65 projects. The highlighted cells (important, but low-scoring goal parameters) are a matter of concern.

					Goal score			Total
			0	25	50	75	100
	Goal	0	144	9	19	19	2	193
	weight		(75%)	(5%)	(10%)	(10%)	(1%)	(100%)
		1	21	35	44	37	10	147
			(14%)	(24%)	(30%)	(25%)	(7%)	(100%)
		2	17	41	142	146	23	369
			(5%)	(11%)	(39%)	(40%)	(6%)	(100%)
		3	10	37	157	254	60	518
			(2%)	(7%)	(30%)	(49%)	(12%)	(100%)
		4	11	28	138	256	65	498
			(2%)	(6%)	(28%)	(51%)	(13%)	(100%)
		5	1	18	57	97	52	225
			(0%)	(8%)	(25%)	(43%)	(23%)	(100%)
	Total		204	168	557	809	212	1,950
			(11%)	(9%)	(29%)	(42%)	(11%)	(100%)

Table 4 :

 4 Spearman's rhos for weights and scores, rho significances of individual goal parameters (n = 65 projects each). The mean weights and mean scores are reproduced here from Table2for convenience.

	Goal parameters (see	Spearman's rho for	Significance of	Mean weights	Mean scores
	Table 1 for longer names)	weight -score	rho p <=	(0-5)	(0-100)
	1 Findability	0.17	0.186	4.00	71.92
	23 Clear communication	-0.19	0.138	3.89	71.54
	22 Info architecture	-0.12	0.335	3.78	71.92
	24 Feedback	-0.02	0.901	3.55	67.69
	9 Quick and easy navigation	0.09	0.482	3.51	71.15
	8 Do primary tasks quickly	0.34	0.006	3.49	71.15
	16 Conceptual model	0.03	0.834	3.45	65.77
	28 Users feel in control	0.17	0.181	3.23	66.15
	12 Complete tasks in time	0.17	0.186	3.18	64.62
	17 Intuitiveness	0.23	0.070	3.12	65.38

Acknowledgements

We thank all the participants who provided data and helped us evaluate the UGT. We thank Dr. Sanjay Tripathi and Prof. SV Sabnis for their help and feedback in the statistical analysis. We thank Prof. UA Athavankar, Prof. Umesh Bellur, and Prof. S Sudarshan of IIT Bombay for their suggestions in this project.