I Dudek

J Y Blaise

A tangible chronology

Keywords: Architecture, Interfaces, Reasoning, Edutainment, Rapid prototyping 1 Introduction

A common task when trying to understand pieces of architecture inside a site is to spot, document and depict changes over time. Quite often successive states of an artefact are then represented using emergent, screen-based computer technologies (Virtual reality, Augmented reality, haptic interfaces, etc.). In this contribution we wish to investigate whether some tasks -both communication in workgroups or reasoning tasks -would not be better tackled once freed from the screen as unique interface. We introduce a proof-of-concept prototype, called "tangible chronology" developed in order to represent changes that occurred on Krakow's market square over a period of 750 years. The paper presents the development and its evaluation, before discussing in what tangible models could serve content holders or academics specifically in historic sciences, and in what their making there calls specific attention and methods.

interface. This paper therefore focuses on a clear research question: can physical models over-perform traditional screen-based virtual models (and naturally in which conditions, for which tasks)? Our contribution introduces a proof-of-concept prototype, called "tangible chronology", developed in order to represent changes that occurred on Krakow's market square over a period of 750 years. The prototype combines a master board, 3D physical models of the artefacts, with a coding of their position on the board and in ordinal time, and a tangible timeline for each artefact.

Figure 1 tangible chronology components: experimenting a move from CAD-based virtual environments to tangibility.

Naturally our aim is not to question the usefulness of computers in general: the tangible models we present come out of a fully computer-operated design and production process. Furthermore, tangible interfaces have become a hot research topic within the computer science discipline itself, and limits of the now traditional HCI devices ("mouse/keyboard/screen") have long been discussed (and exceeded in the gaming industry). We shall therefore not discuss ergonomics on a general ground, but analyse in what tangible models can serve content holders or academics in historic sciences, and in what their making there calls specific attention and methods. In this paper we shall first comment on this global issue, present the prototype, and conclude with possible future directions.

Research context

Over the past 20 years, we have seen the development of a number of technologies that have impacted the way we try to explicit architectural changes over time (changes inside an edifice, changes inside a site). (Mazuryk and Gervautz 1996) or [START_REF] Novák-Marcinčin | Virtual reality technologies and virtual manufacturing in manufacturing engineering[END_REF] give successive overviews of the some of the most commonly used technologies and CAD-based virtual environments such as VR (virtual reality) and AR (Augmented Reality). Although at start focused on design and analysis tasks, computer-based geometric modelling tools little by little integrated a concern for the visual quality of outputs, with realistic rendering layers introduced within many software packages. In short, what we have seen, notably in applications to historical sciences, is the focus progressively shifting from 3D for analysis to 3D for communication. This is particularly obvious when looking back today on contributions dating of the nineties like (Alkhoven,1993) : her analysis of the evolution of Heusden's urban fabric, with a consistent classification effort, sheds light on geometric rules & knowledge in an analytical approach that has little to do with some communication-oriented approaches that the rise of technologies has made possible since then. Under the influence of computer graphics -related fields, of mobile technologies, and of the gaming industry, new ways to deliver the same "virtual world" content have also been introduced -immersive platforms, haptic technology, touchscreen + stylus solutions, mobile devices, etc. It would be irrelevant here to draw the whole history of these technologies, but it appears to us important to state that seemingly, little by little, an idea has made its way inside many circles (wide public, content holders, funding agencies, some scientists, etc.) : if you want to illustrate how an artefact might have been at time t, how it might have been at time t+1, (etc.) , you need comprehensive 3D modelling, and virtual environments (the more the better). But what if you want to understand time, read & compare densities of changes, durations, overlapping, uncertainties? What if you're interested not only in the effects of time on architectural shapes, but in how the whole story developed over time? As food for thinking and debate, let us take a classic example: virtual reality. Is it that virtual? From the point of view of devices, gloves, helmets, captors are certainly not virtual. Now about the content -so-called virtual worlds. Are software, hardware, files virtual? Well in fact preserving such content on the long run is a recurrent issue, and not at all a virtual one. And so at the end of the day what is virtual in a virtual world? Well what is shown is virtual -pieces of architecture, reconstructed or not, i.e. virtual pieces of knowledge about an artefact's evolution. Is this the goal of science? And what has virtual reality to do with reality? If talking about realism in graphics, well then VR is as difficult to understand as reality itself. Furthermore, the actual reality analysts face when producing or processing historical data is partial indications, heterogeneity, uneven distribution of clues in time and space, etc. Is this the information virtual reality helps delivering? (Raposo and al 2008) comment this recurrent issue with this adroitly imprecise quote from [START_REF] Devine | Place and Time: Creating Contextualized Presence for Virtual Heritage[END_REF] "tension between authenticity and completeness" (sic.) Virtual reality might be "close to a reality", but hardly to the reality of our knowledge on the evolution of artefacts. Our reality is packed with doubts, and therefore one should be cautious with what words like "VR technologies" covertly introduce in our practices. Now we do acknowledge these arguments are a bit far-reached. But we believe technologies and corresponding practices are now mature enough to try and weigh cold-bloodedly their actual cost -no offence in that, I suppose. Our position is that 3D technologies in general -not only VR -not only at rendering time neither -invite us to say too much: Too much 3D, too many details, too many choices, too much rendering. And at the same time they do not allow us to say enough: not enough temporal aspects, not enough support for uncertainty and alternatives, not enough context. In other words these technologies, although convincing by many ways, might not be fully suited to the kind of pieces of knowledge and info we would like to communicate: they might not be least the only instrument we should use. And when indeed this instrument needs to be used, we then in return should better understand its cost in terms of relevance, readability and faithfulness in the context of historical analysis, and in terms of cognition for the end user.

Background and related issues

Naturally, our intent is not to question the impact and potential benefits of emergent "virtual worlds" technologies, in particular since we also use them at times [START_REF] Blaise | 3D as a content, 3D as a metaphor[END_REF]. Our intent is to discuss if for some purposes -workgroup discussions, abstract reasoning tasks, acceptability and usability for visually impaired people -we should not put more efforts on alternative solutions. A full range of approaches do exist, in particular in the fields of infovis, positioned by [START_REF] Friendly | A brief history of data visualization[END_REF], in terms of legacy, at the intersection of cartography, and statistics. In cartography [START_REF] Rød | The third choice[END_REF] proposes a brilliant analysis of reality and its representation, quoting for instance Muercke: "the features on the map represent symbolic versions of reality, not reality itself". And so a distance with reality would be welcome? [START_REF] Delaunay | Information spatialisée et déformation cartographique en démographie » In la cartographie en débat : représenter ou convaincre[END_REF] says it in a clear-cut manner: the power of evocation of maps can be found in their capacity to reduce. To this day, at the scale of architecture, what this author calls a reduction process remains ill-formalised. Moreover, when talking about historical sciences, time obviously plays a major role. But here again, at the scale of architecture, time plays a secondary role -with most often a series of states positioned along a timeline. The focus is usually put on "what did my artefact look like at this period of history, and then 200 years later" in a synchronic approach. Other aspects of the time parameter like densities, durations, and rhythms remain poorly dealt with. By contrast, key contributions have emerged in the visual analytics field on how to handle the parameter time in general terms [START_REF] Aigner | Visual methods for analyzing time-oriented data[END_REF], or in the specific context of uncertain data sets [START_REF] Matousek | Extending Temporal Ontology with Uncertain Historical Time[END_REF] [START_REF] Blaise | Visualizing alternative scenarios of evolution in heritage architecture[END_REF].

Motivation and challenges:

Basically our motivation when this research started was to get closer to the reality we handle, and to find some media that, as an end-product, would be relatively free of unevenly mastered technological layers. Tangibility was for us only a track at start, fed by experiences showing physical models, provided that they are adapted to the public, can play a major role in communicating digital content in a more friendly way, as shown for instance by the InterANTARCTICA interactive museum installation presented by (de Bérigny Wall and Wang 2009) or in [START_REF] Thuvander | From the ice age to the present -An audiovisual and tactile model of the swedish region Göta river valley[END_REF]. And indeed, the recent development of rapid prototyping techniques, along with the adoption of de-facto geometrical standards stemming from the industry, opens unprecedented opportunities to rethink the role and impact of physical models. In addition, wireless communication technologies now enable easier interaction between physical models and digital content. It is also important to state that tangibility opens real opportunities for 3D content reuse -a challenge in itself (see [START_REF] Bilasco | An MPEG-7 framework enhancing the reuse of 3D models[END_REF] in particular when looking back on what remains of 20 years of geometric modelling in and around historic architecture. Accordingly, hot research is today emerging on tangible interfaces for all (for the able-bodied as well as for the disabled people -see braillenet.org for instance) in cultural applications, but also in education [START_REF] Lori | TICLE: using multimedia multimodal guidance to enhance learning[END_REF], and more generally in interaction with multimedia content [START_REF] Hirabashi | Tangible 3D interface for sound manipulation[END_REF]. And so at the end of the day tangibility appears as a promising solution, well suited for workgroup activities, relatively technology-free (as far as users are concerned), and what is more bringing in visually impaired people, and people with learning disabilities. Yet in historical sciences time is key to understanding dynamics of change -and making time tangible is a challenge. Time to time transfers (transferring the 750 years evolution of an artefact into 750 seconds) are theoretically possible, but as shown by W.Aigner [START_REF] Aigner | Visual methods for analyzing time-oriented data[END_REF] ill-suited to analytical reasoning since no comparison is possible between events separated in time, or between large numbers of sequences. Furthermore, the readability of such a transfer for the wide public remains to be evaluated. So to which extent is tangibility compatible with constraints one faces in historical sciences, namely reasoning on the parameter time, and handling uncertainty? A physical model can hardly represent the whole evolution of an artefact, and is by definition rather well-determined (at least in terms of geometry). This is precisely the issue behind the tangible chronology prototype: representing through physical models notions like changes (including non-morphological changes), durations and intervals, doubts. From this issue derive the experiment's priorities:

1. one product -several possible audiences, 2. one product -several possible uses, 3. communicate on temporal aspects, 4. handle uncertainty in dating, 5. support workgroup discussions, 6. exhaustive spatial & temporal coverage on a test case. The development and test of the prototype, as will be described in the following section, focuses on these specific challenges.

The tangible chronology prototype

The prototype combines four elements: a masterboard on which 3D physical models of the various evolutions of edifices are positioned, chronocordes that act as a physical equivalent to timelines, and a carved variable values dice. Its specificity lies in tangible codifications used for various purposes, from positioning 3D physical models on the masterboard to confidence assessments. The initial concept, applied to Kraków's medieval market square, was to offer users means to analyse visually and tangibly the site's architectural composition, for any time slot of their choice inside the 750 years covered. To do so users combine on the masterboard 3D physical models corresponding to each edifice's evolution at the period chosen. In other words, users are supposed to be given enough information to combine physically on the masterboard, and to analyse, all possible market squares between 1257 and today (this naturally implies working in discrete time, with a reasonable chrononhere one year -754 combinations). Both spatial information (where was this edifice?) and temporal information (did it exist at the date I am investigating?, if it did exist, which evolution did it reach?) have to be conveyed. Corresponding tangible codifications are at the heart of the prototype: in this section we first describe each code one by one, before presenting possible scenarios of use it finally comes in, and the test case.

Code 1: positioning edifices in space on the masterboard

The first thing needed is to position edifices in space, on the masterboard representing the market place. Each edifice is localised through a univocal and tangible geocode carved in positive beneath the physical model. The geocode is a simple 3 X 3 grid combining flat squares and thick cylinders, measuring approximately 1cm 2 allowing 2 9 combinations. In addition to the grid, the geocode includes a small rectangle, 1cm long, that acts as a positioning pin at assembly time (in order to avoid mirror effects). For each edifice a corresponding geocode is carved in negative on the masterboard, allowing a univocal and fully tangible assembly. For almost each edifice, and therefore for almost each geocode, there are several 3D physical models, corresponding to the successive morphological evolutions of the edifice. There are for instance nine different 3D physical models for the town's hall belfry -one of the three structures that remain standing up to now (the average number of physical model per edifice is between 3 and 4). And so we needed yet another code to distinguish the edifice's first evolution from the second, the second from the third, etc. Taken together, geocode and ordonators are a univocal, time + space, patented assembly system. Yet evolutions of edifices are at this stage only ordered, not dated -no direct relation from edifice to edifice is possible, no mean is given to say which evolution was present at this or that year. A third codification was introduced to deliver more in-depth information on temporal aspects of each artefact's lifeline. ). In the case of events & processes, the position of the shape says "when", the width of the shape says "for how long". • The actual numerical dating (YYYY) is coded through small hemispherical shapes on both sides of the plate if the transformation lasted more than the one-year chronon, on one side only if it lasted less than one year. • The top surface of the plates is engraved with gutter-shaped carvings so as to identify the order of appearance (ordered time) thereby allowing a direct relation of the plate to a given 3D physical model through ordonators (three ordonators <> three carvings) . • Finally, the foremost side surfaces of plates is carved with different iconic-like tangible shapes that represent a qualitative evaluation of the dating's credibility (data stored as numerical scale). At this stage we now can position edifices in space, order then in time, date their changes with, to some extent, an uncertainty assessment. Yet, when talking about uncertainty, besides temporal aspects the morphology has to be taken into consideration (with unknowns of its own). In some cases, the information we have can help state "what kind of edifice" it was in terms of structure and usage but not exactly how many windows it had, or how steep the roof was. And so if we are to question the relevance of tangibility as a media, in the context of weak data sets, we need to learn saying not too much about edifices, with tangible means. Still, as a result of our first evaluation campaign, it appeared clearly that in the case of visually impaired people infos like "how many storeys", "on which side was the entrance" or "what material" could be very useful to deliver in order to foster comparisons. Accordingly, we introduced codifications that say, broadly speaking, "all we know is…" and thereby help us get closer to saying all we know, and nothing more. This clearly calls for further development -and is a challenging issue not only in the context of tangible models.

Code 3: localising changes inside edifices in discrete time

Scenarios of use

Although some issues it raises do call the researcher's attention, the tangible chronology prototype is primarily targeted at use for the wide public, in the context of museums and/or education. It was initialled developed to serve in the context of expert-guided pedagogical activities planned by the MHK (historical museum of the city of Krakow) as part of its extension. Elements presented here above can be combined in three scenarios of use: guided interactive workshops, standalone presentation, board game.

In the guided interactive workshops (museum and / or education) mode, users are invited to recompose the market square for any time t since 1257 under the guidance of an expert who intervenes to comment on the context of the period, the reasons for changes, the historical sources available, the doubts that remain. In this mode all the 3D physical models are laid out on an assembly table, along with their chronocordes. As will be discussed in the evaluation section, the whole installation is part of the educational benefit of the prototype. It favours what in infovis is known as context + focus approach (giving an interactive access, in the same space, to an overall view the chronology of all edifices and to a detailed view on each evolution of each edifice). It has proven to perform extremely well in terms of support for workgroup discussion -an aspect we had absolutely not anticipated, by the way. Furthermore, unlike one-user computer-centred installations, it clearly encourages collaborative group interactions, and is suited to groups of various sizes. But naturally there is a cost to this benefit: such a use requires guidance. Accordingly, there might be more perspectives of applications in the educational field, as part of the pedagogical material through which the teaching is done, than in traditional museums. The prototype can be also laid out as a standalone presentation: 3D models are then positioned with regards to the morphological transformation plates of the chronocorde. Focus is here put on comparative reading, combining temporal + morphological aspects edifice by edifice. Tangible chronology is clearly an edutainment initiative, allowing users not only to perform data mining tasks by touch and vision, but also to perform intuitive assembling tasks (category 3 of the ESAR classification -Exercise play , Symbolic play ,Assembly, games with Rules, see [START_REF] Garon | Le Systeme ESAR: Asted[END_REF] that are particularly fruitful for people that are emotionally vulnerable, or have learning disabilities. Accordingly, we tried to evaluate where the idea of playing with the prototype could lead.

A board game was designed for which a dice with variable values was created. The baseline of the game's scenario is to have gamers get hold of edifices, in relation with dice-dependent time slots, and build an "impossible city" (putting together things that did not coexist in time). This application however goes a bit beyond the scope of this paper and we therefore do not detail it further.

Test case and Production process

As mentioned, our experiment was carried out on the development of Krakow's market square over the past 750 years. Up to 40 structures coexisted at one moment in time or another during that period inside the 200m x 200m market square -yet only three of them remain up to now. Moreover, most of these structures are known to have changed repeatedly, may it be changes in terms of morphology or in terms of usage.

The documentation, the morphology of each evolution, as well as well as the chronology resulted from comprehensive architectural analyses we carried out and published in the past years, with ad-hoc contributions from our colleagues W.Komorowski and T.Weclawowicz. This input comprised dynamic VRML models, formerly used as interfaces in an online documentation platform [START_REF] Dudek | From artefact representation to information visualisation: genesis of informative modelling[END_REF], and a structured description of changes that occurred on each and every edifice during their lifeline [START_REF] Dudek | Understanding changes in historic architecture[END_REF]. Naturally levels of knowledge, and levels of confidence, strongly vary from edifice to edifice, both in terms of morphology and in terms of dating. Furthermore, inside one edifice's chronology, doubts exist here and there, and by the way not necessarily for the oldest period, as demonstrated in [START_REF] Blaise | Visualizing alternative scenarios of evolution in heritage architecture[END_REF]. We transferred the VRML models into physical shapes with some additional CAD modelling needed to integrate the prototype's codification (geocode, ordonators).

The actual physical models produced cover 25 structures, and 90 evolutions : we chose in a first stage to leave aside structures that are too weakly documented -their very existence as independent edifices being even questioned. Accordingly we do not claim we managed to transfer the whole indications we have gathered throughout the years to physical models -we did get closer to the reality of the knowledge we handle, but not exactly to it. The prototype was produced using a rapid prototyping 3D printer from ZCorp. The codification was integrated inside the initial dynamic VRML 3D models so as to avoid dependence to the 3D printer technology. Models were translated into STL format at production time in order to allow geometric checking in the printer-specific software (consistency checking, accuracy, etc.). The chronocorde element however remains "hand-modelled" at this stage -a transitory and unsatisfactory situation.

Evaluation

At mid-development we carried out a first feasibility / readability check with visually impaired people, blind people, people with learning disabilities, thanks to the cooperation of an association specialised on these issues in Kraków. The idea was to evaluate the whole concept and the tangible codifications through informal discussions. A number of positive points were made on the acceptability and accessibility of the prototype, which apparently was a real help for testers to verbalize questions and concern.

However the readability of the architecture itself was questioned at two levels: the size of the edifices "in the real world" (i.e. readability of scale), and a frustration that "you can't touch what's inside the edifice". To the first concern we did react by proposing additional codifications (see section 5.4), but the second obviously requires a change of scale -something we are currently working on, and testing. More generally speaking, this first evaluation brought us to re-think the way we should try and make space sensible for blind people (typically for instance, direct geometric scaling and transfer from reality to 3D physical models can be totally inappropriate since they imply an a-priori knowledge of architectural spaces not necessarily part of their personal experience).

In a second round, we carried out a more structured evaluation with various age groups in a High school in Kraków (VIII PLO). Testers from three classes (ages 14 to 17) were first presented the various components of the prototype (masterboard, 3Dphysical models, chronocordes) and then left, unguided, with precise questions on the development of the market square. Questions required a clear understanding of the information conveyed by the above components. A typical exercise of the evaluation was for instance, given a painting, to date it by its architectural content using the tangible chronology prototype's components. Finally, written comments on the overall system were compiled and discussed informally. Lessons from this evaluation can be summed up as follows:

• the prototype clearly favours questioning and interactivity from the audience,

• at this stage an initial guidance is needed,

• the prototype helps shedding light on the process (interpretation of historical clues) rather than on the results (some set of 3D shapes), • it helps going backwards, back to hints, clues, methods, have them understood by the audience, raises the audience's awareness of historical sciences, • it uncovers differences in levels of knowledge between various elements in a data set, in our experiment an urban ensemble, • It puts temporal aspects on equal terms with spatial aspects. Additionally, and surprisingly in a way at a time when computer gaming is so strong, the board game use raised high interest. More generally, the evaluation proved that saying less, and in a tangible manner, through objects, means leaving more space for interaction and questioning, means more understanding, even fragmental, of what it looks like to face historical data sets -and therefore in what it is challenging, interesting.

Conclusion

This contribution was not about reaching to general conclusions on communicating science, but simply about reporting on an experiment through which we have tried to make the evolution of a site tangible. The tangible chronology prototype, initially designed as an edutainment platform in the context of museum activities, does however underline some more general issues:

• Scientists from the Humanities fields are not condemned to be stamp givers for tech developers blinkered by computation capacities and graphic realism. • In some cases, and in particular in workgroup discussions, traditional "3D Modelling + Virtual environment" solutions are over-verbose solutions, which besides inadequacy to our data prevent users from an appropriation of the challenges behind historical sciences. In short, what the tangible chronology experiment and its evaluation show is that consistency with the underlying data's specificity (temporal aspects, uncertainty) does not undermine scientific communication, it helps it. It has to be said at this stage that for most of it we could have reached this conclusion without experimenting physical models. The prototype shows a succession of discrete states, and emphasizes time / uncertainty parameters -and this can naturally also be done through visual means. IT is not said though that the demonstration that there is more to Historic Sciences than still life 3D my it be (interactive or, animated), probably would not have been as radical. In addition, the experiment has not yet come to its end. In a next step we need to integrate technologies for object-computer interaction (i.e. 3D physical models / chronocordes as tangible interfaces) in order to deliver multimedia digital content. But for this step to be taken (a step at hand in terms of technology) freeing oneself from the screen's attraction is required from many…

Figure 2 .

 2 Figure 2 . Correlating pieces of information in time : the chronographs experiment (Dudek and Blaise 2010) combines variograms (parallel reading of morphological/structural/functional changes), a diachrogram (positions typed states and transitions all along the object's lifeline) and chronologies of features.

Figure 3 .

 3 Figure 3 . Concept and implementation of the geocode.

Figure 4 :

 4 Figure 4 : a number of physical models for each edifice, that need to be ordered in time

Figure 5 :

 5 Figure 5 : tangible codification of ordered time

  For each edifice a sort of tangible timeline called chronocorde positions what happens and when in discrete time (chronon 1 year). A chronocorde features tangible codifications of dates, durations, key dates, uncertainty in dating, and differentiates functional transformations from morphological transformations. It is composed (Figure below) of shapes meaning time (square -turn of the century [a]; cylinder -decade [b]) and of shapes meaning events & processes (thick cylinders -functional transformations [c]; plates -dating of a morphological transformation [d]

Figure 6 :

 6 Figure 6 : Chronocordes -basically a tangible equivalent to the concept of timeline

Figure 7 :

 7 Figure 7: Codification of plates corresponding to morphological transformations

Figure 8 :

 8 Figure 8: Information delivering through tangible codifications (material, levels, entrance orientation).

Figure 9 :

 9 Figure 9: guided workshops use -recomposing the market square at various periods.

Figure 10 :

 10 Figure 10: standalone presentation -a visual comparison of lifelines underling densities and durations of changes.

Figure 11 :

 11 Figure 11: Testing how the prototype supports mining tasks.


Flora Bellone
email: flora.bellone@gredeg.cnrs.fr

Patrick Musso
email: patrick.musso@gredeg.cnrs.fr

Lionel Nesta
email: lionel.nesta@ofce.sciences-po.fr

Stefano Schiavo
email: stefano.schiavo@ofce.sciences-po.fr

Financial Constraints as a Barrier to Export Participation

Keywords: Export, Firm heterogeneity, Financial constraint, Sunk costs JEL Classification : F14, G32, L25, D92

The paper analyzes the link between financial constraints and firms' export decisions, using a large micro-level data set on French Manufacturing firms over the 1996-2004 period.

Our main finding is that firms enjoying better ex-ante financial heath are more likely to start exporting. This results contrasts with the previous empirical literature which found evidence that participation to exports market improves a firm financial health but not that export starters display specific ex-ante financial advantages. By contrast, our result supports the view that financial constraints act as a barrier to export participation. This finding has important policy implications as it suggests that, in presence of financial markets imperfections, public intervention can be called for to help efficient but financially constrained firms to overcome the sunk entry costs into export markets and expand their activities abroad.

Introduction

This paper analyzes the link between firms' export decisions and financial constraints on a large scale longitudinal micro-level dataset. We use as our theoretical background the recent models of firm's heterogeneity and international trade which emphasize the role of sunk entry costs into export markets [START_REF] Baldwin | Hyteresis in import prices : The beachhead effect[END_REF][START_REF] Roberts | The decision to export in Colombia : an empirical model of entry with sunk costs[END_REF][START_REF] Melitz | The impact of trade on intra-industry reallocations and aggregate industry productivity[END_REF] 1 . Once extended to allow for imperfect capital markets, those models offer to financial variables a key role as a determinant of firm export decisions [START_REF] Chaney | Liquidity constrained exporters[END_REF]. Indeed, the existence of sunk entry costs into export markets brings about the question of the financing of such expenditures that, by their very nature, are not matched by contemporaneous receipts. In the presence of financial market imperfections, It may well be -and this is the main research question from which we start-that exporters are those firms who can successfully overcome this financial problem. In fact, this would be consistent with the evidence of exporters outperforming non exporters in several dimensions as shown in the large literature triggered by [START_REF] Bernard | Exporters, jobs, and wages in u.s. manufacturing : 1976-1987[END_REF].

On the other hand, existing empirical literature suggests that exporting may have a beneficial effect on financial constraints, essentially in the form of reducing informational asymmetries by means of some sort of signalling effect or in the form of reducing risk by the diversification benefit of selling in multiple nations [START_REF] Ganesh-Kumar | Outward orientation, investment and finance constraints : A study of indian firms[END_REF][START_REF] Campa | Exporting and capital investment : On the strategic behavior of exporters[END_REF].

The positive impact of export participation on financial health has found its strongest support in a recent contribution by [START_REF] Greenaway | Financial factors and exporting decisions[END_REF] (GGK afterwards). This paper provides the first attempt to evaluate to which extent the self-selection and the ex-post effects drive the correlation between financial variables and firm export decisions. However, the empirical investigations ends up with only support in favor of the ex-post effects.

In what follows we present a new attempt to evaluate the relative importance of self-selection and ex-post effects based on a large panel of French manufacturing firms over the [1996][1997][1998][1999][2000][2001][2002][2003][2004] period. We add on the previous literature by two main respects. First, we propose a new way to measure the degree of financial constraint, base on time-varying, continuous, multidimensional indexes of the access to external finance, which we believe is superior to existing methodologies ; second, we shed new light on the role played by access to external financial resources in shaping firms export decisions.

We can summarize our main findings as follows : First, the relationship between financial variable and export decisions is mainly driven by the negative impact of financial constraints on the decision to start exporting. Second, firms starting to export display a significant exante financial advantage compared to their non exporting counterparts. Third, we do not find significant evidence of any signalling or diversification benefit effects after entry into the export market. This is to say that firms that start serving foreign markets do not improve their financial health as a consequence of exporting. Finally we show that the reasons why our study end up with opposite conclusion compared to the previous literature involve both measurement issues and methodological concerns.

The rest of the paper is organized as follows. Next Section presents an overview of the empirical literature on financial constraints and how they relate to exporting behaviors. Section 3 presents our data and the different measures of financial constraints that will be used in the paper. In Section 4, we present the results of different estimations on the relationship between financial constraints, export decisions, and export status. Section 5 draws the main policy implications of our analysis and concludes.

A glance at the existing literature

Since the late 1980s a large number of empirical studies have addressed the issue of financial constraints, mainly in order to study the relation between firms investment and the availability of internal funds. Indeed, a large and convincing evidence exists showing that when a standard investment equation is augmented with cash flow availability, the fit of the equation is improved. Now, under perfect capital markets, internal and external sources of financial funds should be perfectly substitutable [START_REF] Modigliani | The cost of capital, corporation finance and the theory of investment[END_REF], so that the availability of internal funds should not affect investment decisions.

While there is a substantial consensus on the notion that liquidity does matter in investment equations, much less agreement exists on why this is the case. [START_REF] Chirinko | Why does liquidity matter in investment equations ?[END_REF] suggest two possible hypotheses : the existence of financial constraints (due to the existence of either asymmetric information or transaction costs), and mere mispecification whereby liquidity takes up the effect of other omitted variables. In particular, contrasting empirical evidence exists on the notion that investment responsiveness to cash-flow implies the existence of financial constraints.

Measuring financial constraints

The usual empirical strategy adopted to detect the existence and the relevance of financial constraints entails segmenting the sample into subgroups of firms with different likelihood of facing financial constraints. Thus for instance, [START_REF] Fazzari | Financing constraints and corporate investment[END_REF] claim that firms with low dividend payout ratios (likely constrained) display higher investment-cash flow sensitivity. A number of subsequent studies tend to find supporting evidence using a number of different variables to identify constrained firms [START_REF] Bond | Dynamic investment models and the firm's financial policy[END_REF][START_REF] Gilchrist | Evidence on the role of cash flow for investment[END_REF][START_REF] Chirinko | Why does liquidity matter in investment equations ?[END_REF].

The first paper finding opposite results is, to the best of our knowledge, [START_REF] Devereux | Investment, financial factors and cash flow : Evidence from U.K. panel data[END_REF] which reports a higher cash flow coefficient for larger firms, even after controlling for sector heterogeneity. But it is only with the work by [START_REF] Kaplan | Do investment-cash flow sensitivities provide useful measures of financing constraints ?[END_REF] that the usefulness of investment-cash flow sensitivity as a measure of financial constraint has been definitely questioned. Exploiting qualitative information from financial statements of firms classified as constrained in [START_REF] Fazzari | Financing constraints and corporate investment[END_REF], the authors show that firms appearing as less constrained display substantially higher investment-cash flow sensitivity. Hence, they conclude, the latter can no longer be regarded as a useful measure of financial constraint. Since then, other authors have reported evidence of a negative relation between investment-cash flow sensitivity and financial constraints (for instance [START_REF] Kadapakkam | The impact of cash flows and firm size on investment : The international evidence[END_REF][START_REF] Cleary | International corporate investment and the relationships between financial constraint measures[END_REF].

To overcome the weakness of the degree of investment-cash flow sensitivity as a measure of financial constraints, alternative strategies have consisted in placing firms in two different groups on the basis of some arbitrary threshold such as median values, or first quartiles [START_REF] Devereux | Investment, financial factors and cash flow : Evidence from U.K. panel data[END_REF][START_REF] Gilchrist | Evidence on the role of cash flow for investment[END_REF][START_REF] Greenaway | Do financial factors affect exporting decisions ?[END_REF][START_REF] Cleary | International corporate investment and the relationships between financial constraint measures[END_REF].

Other authors use a finer classification and classify firms in three or more groups [START_REF] Fazzari | Financing constraints and corporate investment[END_REF][START_REF] Kadapakkam | The impact of cash flows and firm size on investment : The international evidence[END_REF][START_REF] Kaplan | Do investment-cash flow sensitivities provide useful measures of financing constraints ?[END_REF]. Almost all the papers rely on a limited list of variables such as size, age, dividend policy, membership in a group or conglomerate, existence of bond rating, and concentration of ownership. All these variables are ment to capture source of informational asymmetries that can potentially constrained access to capital markets. So, for instance, [START_REF] Fazzari | Financing constraints and corporate investment[END_REF] claim that dividends are a residual decision in firms strategy and, under the assumption that external finance is more costly than internal funds, paying high dividends in presence of profitable investment opportunities is not consistent with profit maximization. Hence, high dividend payout ratios signal the absence of financial constraints. Big and mature firms are likely to find easier access to external funds as it should be easier to collect information on them compared to young and small enterprises.

Similarly, membership in a larger conglomerate should facilitate market access both because of the signaling exercised and because the single firm can likely receive funds from its headquarter. Also, the mere existence of a bond rating (even irrespective of the rating itself) can signal a commitment of the firm vis-à-vis financial markets. In a similar vein the existence of a dominant shareholder is seen as a way to reduce agency problem with management and therefore to act as a guarantee toward external investors. Other papers, namely [START_REF] Becchetti | The determinants of growth of small and medium sized firms. The role of the availability of external finance[END_REF] and [START_REF] Savignac | The impact of financial constraints on innovation : evidence from French manufacturing firms[END_REF], use survey data whereby firms themselves give a self-assessment of their difficulty to access external financial funds.

There are a few weaknesses related to the above strategies. First, [START_REF] Hubbard | Capital-market imperfections and investment[END_REF] notes how most of the chosen criteria tend to be time invariant whereas one can imagine that firms switch between constrained or unconstrained regimes depending on overall credit conditions, investment opportunities and idiosyncratic shocks. Second, all works relying on dividend payments are restricted to quoted firms which, at least for what concerns continental Europe, tend to be large and mature. As a further potential problem, we add that all the above studies rely on a unidimensional definition of financial constraint, i.e. they assume that a single variable can effectively identify the existence of a constraint, and the latter is viewed as a clear-cut phenomenon that is either in place or not, without allowing for different degrees. Notable exceptions are the works by [START_REF] Lamont | Financial constraints and stock returns[END_REF], [START_REF] Cleary | The relationship between firm investment and financial status[END_REF][START_REF] Cleary | International corporate investment and the relationships between financial constraint measures[END_REF], an [START_REF] Whited | Financial constraints risk[END_REF]. The first paper builds a multivariate index that builds on [START_REF] Kaplan | Do investment-cash flow sensitivities provide useful measures of financing constraints ?[END_REF] whereby five variables are weighted using regression coefficients in the [START_REF] Kaplan | Do investment-cash flow sensitivities provide useful measures of financing constraints ?[END_REF] paper and collapsed into a single indicator. 2 The main difficulty with this approach is the need to extrapolate results obtained on a small sample of 49 US quoted firms (those used in [START_REF] Kaplan | Do investment-cash flow sensitivities provide useful measures of financing constraints ?[END_REF] and apply them to a larger population (and in a different period). Furthermore, one of the variables needed to compute the index is Tobin's Q, whose use as a proxy for investment opportunities is rather controversial and lies at the core of the investment-cash flow debate outlined above. [START_REF] Whited | Financial constraints risk[END_REF] take a similar route but perform their own estimate and base their index on a structural model whereby they measure financial constraints by means of the shadow price of capital. 3

Another interesting attempt to develop a time-varying, continuous measure of financial constraints is due to [START_REF] Cleary | The relationship between firm investment and financial status[END_REF], which uses multiple discriminant analysis (in a way similar to Altman, 1968) to compute a score based on six variables. 4 The methodology entails two steps : first one needs to classify firms as constrained or unconstrained according to some characteristic, second the statistical analysis is performed which delivers a coefficient for each of the (six) control variables. 5 The score is then obtained as the predicted value of the empirical model, and it can be applied also to firms excluded from the first step of the analysis. To separate firms [START_REF] Cleary | The relationship between firm investment and financial status[END_REF] makes the hypothesis that firms reducing dividend payments one year to the next, are likely to be financially constrained, whereas those augmenting them are likely not to be constrained. Firms keeping dividend payment constant are not used in the multiple discriminant analysis, but later they are nonetheless attributed a score. 6 2 The variables are (i) cash flow to fixed assets, (ii) market to book ratio, (iii) debt to total assets, (iv) dividends to fixed assets, and (v) cash to fixed assets.

3 The variables included in the model are (i) the ratio of long-term to total debt, (ii) a dividend dummy, (iii) sales growth (both for the individual firm and the sector), (iv) (the log of) total assets, (v) the number of analysts following the firm, (vi) the ratio of liquid to total assets, (vii) the industry debt to assets ratio. 4 There are (i) the current ratio, (ii) the debt ratio, (iii) the fixed charge coverage, (iv) the net income margin, (v) sale growth, and (vi) slack over total assets. See [START_REF] Cleary | The relationship between firm investment and financial status[END_REF] for a definition of the variables. 5 This is very much similar to what a probit or a logit estimation would do. In fact, multiple discriminant analysis is nothing more than an ancestor of these methodologies, which, because of current computer power, are probably preferable as more robust .

6 An obvious requirement of this methodology is working with quoted firms. In principle one could then derive a score for non quoted firms as well, but it is not clear how well the index would then behave.

Financial constraints and export decisions

In presence of imperfect capital markets, one can figure out at least two rationales of why exporting firms should be less financially constrained than non exporting firms : one stressing the link going from financial constraints to export behaviors, the other assuming that causality runs in the opposite direction.

First, if firms have to incur large sunk entry costs to enter into export markets, financially constrained firms may be less able to cover those costs compared to unconstrained firms. this implies that only less constrained firms will be able to start exporting. This simple idea is formalized in [START_REF] Chaney | Liquidity constrained exporters[END_REF] which adds liquidity constraints to a model populated by heterogeneous firms differently engaged in international trade (à la [START_REF] Melitz | The impact of trade on intra-industry reallocations and aggregate industry productivity[END_REF]. His model echoes the growing set of evidence according to which a large part of trade barriers take the form of fixed costs which must be paid up-front. A growing body of empirical literature documents significant hysteresis effects associated with firms' export participation and interprets this as signalling the relevance of sunk entry costs. 7 In the business literature, [START_REF] Moini | Export behavior of small firms : The impact of managenial attitudes[END_REF] reports results form a survey among US non exporters, where firms claim their primary obstacle to initiate an export program is the presence of high up-front costs.

Second, the very fact of exporting can generate an advantage in terms of access to external financial funds. This can be rationalized in different ways : (i) exporting firms may generate more stable cash flows, as they benefit from international diversification of their sales [START_REF] Campa | Exporting and capital investment : On the strategic behavior of exporters[END_REF] ; (ii) selling in international markets can be considered as a sign of efficiency and competitiveness by domestic financial markets, so that exporting lowers the informational asymmetries that lie behind financial constraints [START_REF] Ganesh-Kumar | Outward orientation, investment and finance constraints : A study of indian firms[END_REF] ; (iii) foreign exchanges revenues may represent a better collateral to access external funds in foreign financial markets [START_REF] Tornell | Credit market imperfections in middle income countries[END_REF]). 8

In particular, [START_REF] Campa | Exporting and capital investment : On the strategic behavior of exporters[END_REF] postulate a link going from exporting to financial constraints : exporters, their arguments goes, enjoy a more stable flows of revenues because they sell their products in markets whose business cycles are not perfectly correlated. Also, exporting being associated with better performance, firms engage in international activities send a 7 See [START_REF] Roberts | The decision to export in Colombia : an empirical model of entry with sunk costs[END_REF] for Colombia, [START_REF] Bernard | Export, entry, and exit by German firms[END_REF] for Germany, [START_REF] Campa | Exchange rates and trade : How important is hysteresis in trade ?[END_REF] for Spain, [START_REF] Bernard | Why some firms export[END_REF] for the US. [START_REF] Das | Market entry costs, producer heterogeneity, and export dynamics[END_REF] go one step further and estimates a structural model to quantify sunk costs. They conclude that entry costs into export market are substantial.

8 It is noticeable that, in specific economic environments, the fact of exporting can generate a disadvantage instead of an advantage in terms of financial health. For instance, [START_REF] Espanol | Why exporters can be financially constrained in a recently liberalised economy ? a puzzle based on argentinean firms during the 1990[END_REF] works with a panel of Argentinean firms and she documents an inverse relationship whereby exporting firms are those facing larger constraints.

She argues that this can be explained by the specific macroeconomic context of the 1990's in Argentina : the appreciation of the currency which followed financial liberalization may have triggered a profit squeeze for exporting firms, and weakened their balance sheet (diminishing both sales and asset accounts). As a consequence, not only it reduced internal finance but also increased the probability of bankruptcy, therefore reducing banks' willingness to lend to exporting firms.

reassuring signal about their 'type' to the market. Both these effects should grant easier access to external finance to exporting firms. Empirically, Campa and Shaver show that investment is less sensitive to cash flow for the group of always exporters compared to the group of never exporters. Considering next the remaining group of firms which shift their export status during the period of investigation, they show that financial constraints are more binding for those firms when they do not export compared to when they do export. Nonetheless, the [START_REF] Campa | Exporting and capital investment : On the strategic behavior of exporters[END_REF] results suffers from a few shortcomings. First, in using the sensitivity of investments to cash-flows, Campa and Shaver are directly confronted to the [START_REF] Fazzari | Financing constraints and corporate investment[END_REF] critic which casts strong doubt on the usefulness of this financial constraints measure. Second, if both the diversification and the signalling channels were important, one should observe a positive correlation between the share of firms' foreign sales and their ability to overcome financial constraints.

Hence, export intensity rather than export status should be the most influential determinant of a reduction of the constraint, but Campa and Shaver fail to find such a relationship. finally, as they do not control for firm-level heterogeneity in productivity, they cannot rule out the possibility that an independent change in productivity cause altogether the decision of exporting and the lessening of the financial constraints.

In a recent paper, [START_REF] Greenaway | Financial factors and exporting decisions[END_REF] propose a more accurate assessment of the relationship between financial constraints and export decisions. Working with a large scale panel of UK manufacturing firms over the 1993-2003 period, they explicitly test for the causality running between the two variables. Improving on Campa and Shaver in the way they measure financial constraints (actually using a segmenting variable -the liquidity ratio or the leverage ratio-instead of using the sensitivity of the firms' investments to cash-flows), they conclude in favor of the causality running from export to financial health. In other words, they find no evidence in favor of the self-selection hypothesis but strong evidence in favor of ex-post effects.

However, the way GGK identify financial constraints also raises some issues as the authors select, among a number of financial variables used to identify the constraint, those that better discriminate among exporters and non exporters. Therefore, they risk ending-up with a built-in relation between their index of financial constraint and the probability of becoming an exporter. 9

3 Data and methodology

Data sources : the EAE survey and the DIANE database

We use data from two main sources. Both of them collect information on French firms, though their coverage is somehow different. The first (EAE ) is a survey that gathers information from the financial statements and balance sheets of all individual manufacturing firms with at least 9 The details on the choice of the variables used to measure the degree of financial constraints faced by the firms are not presented in [START_REF] Greenaway | Financial factors and exporting decisions[END_REF] paper but have to be found in a companion paper [START_REF] Greenaway | Do financial factors affect exporting decisions ?[END_REF].

20 employees, from 1990 to 2004. 10 Each unit is endowed at birth with an identifying number that allows us to track the firm over time. The second source of information is the DIANE database published by Bureau van Dijk, which collects data on over 1 million French firms for the period 1996-2005. This database provides us with many financial stock variables absent from the EAE survey. Merging the two datasets yields around 83,000 firm/year observations, stemming from an unbalanced panel of over 12,500 manufacturing enterprises followed over the period 1996-2004. 11

The index of financial constraints

The way financial constraints are measured is a very sensitive issue in the literature which investigates the link between financial variables and firms' investment decisions. Measurement issues may be important as well in the new literature on the relationship between financial variables and firms' export decisions. In this paper, we propose to confront four different measures of financial constraints.

The two first indexes are the liquidity ratio and the leverage ratio. 12 Both measures inform about the general financial health of a firm but may have some weakness as an index of financial constraints as they rely on a single variable to classify firms ex ante. In other words, they are unidimensional measures of financial constraints.

Therefore, we also rely on indexes which attempt to collapse information coming from different variables which convey important information relative to the existence of financial constraints. The indexes are built following the methodology initially proposed by [START_REF] Musso | The impact of financial constraints on firms survival and growth[END_REF] (which in turn build on [START_REF] Cleary | International corporate investment and the relationships between financial constraint measures[END_REF]. The 7 variables chosen to enter into the indexes are selected on the basis of their performance in existing studies, and their perceived importance in determining ease of access to external financial funds. They are : size (measured by total assets), profitability (return on total assets), current ratio (current asset over current liabilities ), cash flow generating ability13 , solvency (own funds over total liabilities, measuring the ability by a firm to meet its long-term financial obligations), trade credit over total assets and repaying ability (financial debt over cash flow).

For each of these 7 dimensions, and each year, we first compute the value of the firm relative to the average of all firms belonging to the same 2-digit NACE sector, and then place it in 10 The survey (Enquête Annuelle d'Entreprises) is conducted by the French Ministry of Industry. The surveyed unit is the legal (not the productive) unit, which means that we are dealing with firm-level data. To investigate the role of financial constraints on growth and survival, firm, rather than plant level data seem appropriate.

11 [START_REF] Chirinko | Why does liquidity matter in investment equations ?[END_REF] note that focusing on manufacturing only -as it is often done in the literaturemay exaggerate the role played by financial constraints because of the specialized nature of the assets involved with those firms.

12 The liquidity ratio is defined as the firm's current assets minus its short-term debt over total assets, and our leverage ratio as the ratio of the firm's short-term debt to current assets.

one of the quintiles in which the resulting distribution is divided.14 Hence, for each firm/year observation we end up with 7 scores ranging from 1 to 5, with 1 containing the smallest values. This information is then combined in different ways to obtain a synthetic index, which is then rescaled to have a common 1-10 range, with smaller values being associated with more constrained firms. In what follows we concentrate on two ways to combine the information : (i) a simple sum of the 7 scores (Score A) ; (ii) the number of dimensions for which the firm/year lies in the first or second quintiles (Score B) 15 .

The correlations between these four measures of financial constraints are presented in Table 1 below. It is noticeable that unidimentional measures and multidimensional ones, while positively correlated, clearly encompass different information. On the other hand, the liquidity ratio displays almost the same information than the leverage ratio as do Score A compared to Score B.

[Insert Table 1 here]

Measures of firm productivity

In what follow, we compute Total Factor Productivity (TFP) using the so-called Multilateral Productivity Index first introduced by [START_REF] Caves | Multilateral comparisons of output, input, and productivity using superlative index numbers[END_REF] and extended by [START_REF] Good | Index number and factor demand approaches to the estimation of productivity[END_REF].

This methodology consists of computing the TFP index for firm i at time t as follows :

ln

T F P it = ln Y it -ln Y t + t τ =2 ln Y τ -ln Y τ -1 -     N n=1 1 2 (S nit + S nt ) (ln X nit -ln X nt ) + t τ =2 N n=1 1 2 (S nτ + S nτ -1 ) (ln X nτ -ln X nτ -1 )     (1)
where Y it denotes the real gross output of firm i at time t using the set of N inputs X nit , where input X is alternatively capital stocks (K), labor in terms of hours worked (L) and intermediate inputs (M ). S nit is the cost share of input X nit in the total cost. 16 Subscripts τ and n are indices for time and inputs, respectively. Symbols with an upper bar correspond to measures for the reference point (the hypothetical firm), computed as the means of the corresponding firm level variables, for all firms, in year t. This methodology is particularly well suited to comparisons of within firm-level panel datasets across industries in that it guarantees the transitivity of any comparison between two firm-year observations by expressing each firm's input and output as deviations from a single reference point. those which always export (Continuous Exporters) during the whole period, those which do no export initially but become exporters between 1993 and 2004 and continue to export ever since (Export Starters), and those concentrating exclusively on the domestic market (Never Exporters).

Descriptives Statistics

[Insert Table 2 here] Consistently with the literature on export and productivity, we observe a clear ranking between exporters and non-exporters. Specifically, firms which export (either continuous exporters or export starters) tend to be larger, more efficient and less financially constrained than never exporting firms. 17

The largest gaps are between the continuous exporters and the never exporters, whereas the difference between starters and never exporters is much smaller (apart from average productivity). On average, firms belonging to the former group are 27% times more liquid (and their leverage ratio is 11 % lower) than non-exporting firms. In terms of our Credit constraints indexes (Score A et B), the ranking of continuous exporters is respectively 7% and 6% higher.

It is also noticeable that our four financial constraints measures offer a consistent ranking. For each index, on average, continuous exporters are less financially constrained than export starters which themselves are less financially constrained than never exporters.

Empirical Results

We start our econometric analysis by investigating the role of financial constraints in determining the probability of exporting next period. In this inquiry, all types of exporting firms (namely, continuous, starters and switchers) are pooled altogether. We then restrict our sample to export starters and never exporters in order to investigate further causality issues.

The probability of exporting

We regress the probability of exporting in time t as a function of the degree of financial constraint in t -1. We use a large number of controls, including lagged size, wage, and productivity along with industry 18 and year dummies. Specifically, we estimate :

17 Remember that our Scores measure ease of access to external finance so that larger values imply a lower constraint. Liquidity ratio, Leverage ratio, Score A, and Score B.

In order to check the robustness of the coefficients on financial variables, we present the results obtained from two different estimators : a Random-Effects Probit estimator, and a Fixed-Effects Linear Probability Model. Moreover, we run the estimations for each of the four alternative financial constraints measures. Finally, we augment the initial Equation 2 with, as an additional control, the lagged dependent variable. This dynamic specification allows us to take into account hysteresis in export market participation. We want to investigate if, once hysteresis is controlled for, the degree of financial constraints in t -1 still impact the decision of exporting in t. For the dynamic specification, we also run two different estimations : a dynamic Random-effects Probit model and a dynamic Fixed-Effects Linear Probability model. We end up with two tables, table 3 andtable 4, respectively for the static specifications and for the dynamic specifications.

[Insert Table 3 here] [Insert Table 4 here]

For each estimation, all control variables are significant and display the expected sign. In particular, the size dummies are larger in absolute value for the smallest firms, indicating that smaller firms are less likely to export than larger ones. The wage and productivity variables have a positive effect on the probability of being an exporter, consistently with the fact that exporting firms tend to pay higher wage and to be more efficient. Firms with subsidiaries (either at home or abroad) are more likely to export, suggesting some additional motive for exporting of those firms even after controlling for their other favorable characteristics.In the dynamic specifications, the coefficients on the lagged dependent variable are high and significant while the value the coefficients on each of the other controls decreases. Nonetheless, each coefficient still displays its expected sign and is significant. This means that, whatever the current export status of the firm, its contemporaneous characteristics still impact its future export decision. 19 In comparison, the evidence on the impact of the financial variables are more mixed. On the one hand, each of the unidimentional measures (the liquidity ratio or the leverage ratio) displays the expected sign and is significant. In other words, good financial health (high liquidity or low leverage) in t -1 increases the probability of being an exporter in t. Moreover, this results still holds in the dynamic specifications 20 . On the other hand, the multidimensional financial constraints indexes (either Score A or Score B) do not produce consistent results with the liquidity or leverage ratios. In neither of the 16 estimations, do Score A or Score B display a positive and significant coefficient.

At this stage, our results cast some doubts on the effectiveness of the link between financial variables and the decisions to export : if multidimensional indexes are more reliable measures of financial constraints than unidimentional ones, one should be concerned by the fact that the coefficient on Score A et B lose their significance when controls are included in the regressions. 21 This could indicate that financial markets are efficient enough for financial constraints not impacting the export decisions of firms.

However, another possible explanation is that financial variables do not impact in the same way on continuous exporters and export starters. Suppose, for instance, that financial constraints only impact the decision to start exporting but have no additional impact on the export decisions of established exporters. Hence, it is possible that the coefficient of our financial constraint index is not significant in the overall sample because of a sort of composition effect.

To specifically investigate this hypothesis, we relate our financial constraints indexes to the firm decision to start exporting. We want to check whether only those firms that are relatively less constrained can afford to pay the sunk entry cost in export markets and therefore start seeling abroad.

To do so we proceed in two steps. First, we examine whether future exporters have an exante financial advantage compared to non exporters. Then, we provide a formal analysis of the decision to start exporting.

The ex-ante financial advantage of future exporters

As a preliminary issue, we investigate whether future exporters display an ex-ante financial advantage over their non exporting counterparts, namely firms belonging to the same industry 19 That is to say that, among today exporters, large firms which pay high wage and which display relatively high productivity are still the more likely to pursue exporting tomorrow. 20 Once more, the coefficients on both ratios are lower than in the static specifications but they are still significant. This means that among today exporters, the more liquid (less leveraged) firms are still the more likely to pursue exporting tomorrow. 21 We indeed checked that without size, Wage and TFP as control variables, Score A and B display significant coefficients with the expected positive sign. These results are available upon request.

and share similar characteristics in terms of size and efficiency. We use a specification adapted from the standard [START_REF] Bernard | Exceptional exporter performance : Cause, effect, or both ?[END_REF] methodology. We consider the group of firms which start to export between 1999 and 2004. We then compare their degree of financial constraint with the one of their never exporting counterparts. The comparison is done one and three years before entry into the export markets. Specifically, we estimate :

ln F inconst i,t-s = α + βExportdum it + γZ i,t-s + dummies + ε it (3)
where F inconst is alternatively one of our four measures of financial constraints, Exportdum is the dummy for exporter status, and Z a vector of controls that comprises Size (as measured by Employment), productivity (T F P ), profitability (operating income over total assets), and a set of industry-year dummies.

It must be emphasized that Equation 3does not test for a causal relationship. It rather allows to evaluate the strength of the pre-entry premium -i.e. to see to what extent firms that export in time t were already less constrained some times prior the entry-by means of a simple t-test on the significance of the β coefficient. Results are presented in table 5.

[Insert Table 5 here]

The coefficient of the export dummy is positive and significant in almost all cases, backing the idea that before entering into foreign markets, future exporters enjoyed easier access to external financial funds. One year before, export starters are around 36% less constrained than their non exporting counterparts (in terms of Score A or Score B). The financial advantage of future exporters is less pronounced in terms of the liquidity ratio and of the leverage ratio. This results is consistent with the idea that liquidity and leverage ratios, even though they inform on the financial heath of a firm, may be less consistent indexes of the ability of a firm to access external finance than multidimentional indexes as Score A and B.

We performed the following robustness tests. First, we run the same regressions excluding switching firms from our sample. This implies eliminating all firms that do start exporting during the period under consideration, but do not continue to serve export markets ever since.

Hence, we reduce the number of entries into foreign markets to "successful entries" only. Results are presented in table 9 of Appendix A : the estimated coefficients are lower but, in almost all cases, robust to the change of sample. Second, we implemented the specification which led GGK to reject the self-selection hypothesis for their UK dataset. 22 Results are presented in Table 12 of Appendix B. We end up with results very consistent with the previous literature.

Indeed, implementing the GGK empirical strategy leads us to reject the hypothesis that futures exporters displays an ex-ante financial advantage over non exporters. This leaves us with the 22 Indeed, we wonder to which extent the discrepancies between the results presented by GGK and ours are driven by differences in the datasets, by the financial variable used, or by the empirical strategies.

issue of which specification should be preferred ? In our view, specification 3 has one main advantage : it investigates the ex-ante financial advantage at different points in time rather than on the average values taken over the whole pre-entry period (as in GGK). This allows us to take into account the fact that the degree of financial constraints faced by a firm is timevarying. A manager who think about expanding his firm activities abroad can decide to delay the firm entry into export markets if the firm is financially constrained. This manager could find rational to wait until the financial constraints of the firms have been lessened to start exporting.

In such a scenario, averaging the financial constraints index of the firm over the whole pre-entry period could lead to misleading results.

The decision to start exporting

In this section, we ask if among the today non exporting firms, the ones which will decide tomorrow to expand their activity abroad are the less financially constrained ones. In other words, we investigate the impact of financial variables on the decision to start exporting rather than on the mere decision to export as it was done in Section 4.1 above. We intervene on the dependant and explanatory variables in Equation 3 : i.e instead of regressing the financial constraints on the future export status, we regress the future export status on the financial constraints. Specifically, we use the subsample of Export starters and Never exporters23 , and estimate :

Expdum it = a 0 + a 2 Size i(t-1) + a 3 T F P i(t-1) + a 4 F inconst i(t-1)

+ industry + time + ε it (4)
where Expdum, F inconst, and T F P are defined as before. In this specification, firm size is controlled for by its employment (number of hours worked). Results are presented in Table 6.

[Insert Table 6 here]

We find that the coefficients on the Financial Constraints indexes are all positive and significant in the regressions which investigate the impact of one year lagged financial constraints index on the decision to start exporting in t. On the other hand, the coefficients lose their significance when the financial advantage is estimated 3 year before the entry into export market. This is consistent with the idea that it is the short-run availability of external finance which is determinant in the decision to enter for the first time new foreign markets.

Detecting Ex-post effects

In this section we present an empirical assessment of the extent to which exporting firms benefit from their activities abroad in terms of access to external finance. Once again we use specifications adapted from [START_REF] Bernard | Exceptional exporter performance : Cause, effect, or both ?[END_REF] to investigate whether firms' financial constraints go down after their entry into foreign markets. We examine exporter and nonexporter levels and growth rates over short and medium intervals for our four measures of measures of Financial constraints. Specifically, we estimate :

F inconst i,t+s = α + βExportdum i,t + +γX i,t+s + ε i,t (5)
and

∆F inconst i,t/t+s = α + βExportdum i,t + γX i,t + ε i,t (6)
where ∆s identify growth rates between time t and t + s.

Hence, we test whether after starting to export firms experience a change in their access to external finance that is not explained by a contemporaneous change in size, profitability and productivity. Results are presented in tables 7 and 8 below.

[Insert Table 7 here]

[Insert Table 8 here]

We don't find any evidence to support a beneficial effect of exporting in the position of the firm vis-à-vis external investors. In the regression in levels, the estimated coefficients of the export dummy are positive and significant in the short-run interval only for the leverage ratio and Score A. On a longer horizon, none of them is significant whatever the measure of financial constraints. Moreover, when one considers growth rates (instead of the levels) none of the coefficients on the export dummy is significant.

Here again we performed different robustness checks. Results are robust to the exclusion of switching firms (see table 10 and 11 in Appendix A). We also replicate the specification which led GGK to conclude in favor of the presence of ex-post gains. This specification consists in comparing average levels of the financial constraints indexes 24 instead of comparing those levels in specific point in time (as in Equation 5), or instead of comparing their growth rates (as in Equation 6). When implementing the GGK specification on our dataset, we also find positive and significant ex post effects (see results in 13 of Appendix B). However, our preferred specification remains the ones implemented in this section. Indeed, in the case where Export starters are already financially advantaged before starting to export, the GGK specification does not allow to investigate whether exporting involves additional gains in terms of financial health. Only a test of the change in the financial constraints indexes as performed in Equation 6can support the hypothesis of ex-post benefit 25 .

24 the average is computed over 3 to 4 years after the entry into export markets 25 And even so, the test is still inconclusive. Indeed, suppose there is a firm that experiences favorable shocks

Conclusion

In this paper, we investigated the link between financial constraints and firms' export decisions. We used different measures of financial constraints that take into account the complex nature of this phenomenon. The literature presents two different views of the relationship between export and financial constraints : one stresses the fact that constrained firms will not be able to afford the up-front costs associated with entry into a new market, the other suggests that exporting act as a signalling device and therefore exporting firms will benefit from a better access to external financial funds. In this paper, we presented an attempt to discriminate among the self-selection and the signalling or diversification benefit hypotheses based on a large panel of French manufacturing firms. Our main finding is that 'self-selection' occurs : among all today non exporters, only less constrained firms decide to start exporting in the next one to three years. On the contrary, we do not find significant evidence that firms becoming exporters do not experience a reduction in their constraint as a consequence of exporting. All in all, we conclude that our data support the recent models of firm's heterogeneity and international trade which emphasize self-selection into export markets in a context of financial market imperfections. In those models, public intervention can be called for to help efficient but financially constrained firms to overcome the sunk entry costs into export markets and expand their activities abroad.

In this perspective, our results can be seen as justifying the export promotion policies which have flourished in most of the industrialized countries since the late of the 1990s and early 2000s and which mainly consist in helping small and medium size firms to overcome the fixed entry costs into export markets.

A Appendix A : Self selection and ex-post effects : results without switchers

In this appendix, we present the results of regressions run of a sample of firms which excludes switching firms. We present both the self-selection equation (Specification 3 in section 4.2) and the ex-post equations both in levels and in growth rates (Specifications 5 and 6 in section 4.4))

[Insert Table 9 here]

[Insert Table 10 here]

[Insert Table 11 here] A Appendix B : A replication of [START_REF] Greenaway | Financial factors and exporting decisions[END_REF] The specifications implemented by GGK also borrow to [START_REF] Bernard | Exceptional exporter performance : Cause, effect, or both ?[END_REF].

Concerning the test of the self-selection hypothesis, the specification requires to consider only the group of firms which export in the final year t = T of a given period of time [0; T ]. This period is alternatively the entire time period 1996-2004 or subperiods, 1996-2000 and 2001-2004. All other firms are then dropped form the sample expect the ones which never exports within the whole period [0; T ]. This later group is the control group. We next perform a test based on the average values of the financial constraints measure for both groups of firms over the period [0; T -1] and investigate whether those values differ in favor of the group of Export starters.

Specifically, we estimate :

1 T -1 T -1 0 ln X i,t = α + βExportdum iT + δD i + γSize i,0 + ε it (7)
where D i is a set of Industry dummies and Size a variable which control for the firm' initial size, measured in terms of employment(number of hours worked). The results are displayed in table 12.

[Insert Table 12 here] Concerning the test of the presence of ex-post effects, the specification requires to consider the group of firms which start to export in the initial year t = 0 of a given period of time [0; T ]. This period is alternatively the entire time period 1996-2004 or subperiods, 1996-2000 and 2001-2004. All other firms are then dropped from the sample except the ones which never export within the whole period [0; T ]. This later group is the control group. The test consists in comparing the average values of the financial constraints levels for both groups of firms over the period [1; T ] and in investigating whether those levels differ in favor of the group of Export

starters 26 . 1 T -1 T 1 ln X i,t = α + βExportdum i0 + δD i + γSize i,0 + ε it (8)
where D i and Size are defined as before. The results are displayed in table 13.

[Insert Table 13

(3)

(5)

(2)

(3)

(5)

(2)

(3)

(2)

(3) Tab. 9 -Self-selection into export markets : results excluding switchers

(2)

(3)

(2)

(3) Standard errors in brackets significant at 10% ; ** significant at 5% ; *** significant at 1%

  066]*** [0.066]*** [0.067]*** [0.067]*** [0.008]*** [0.008]*** [0.008]*** [0.008]062]*** [0.062]*** [0.062]*** [0.062]*** [0.007]*** [0.007]*** [0.007]*** [0.007]060]*** [0.060]*** [0.060]*** [0.060]*** [0.007]*** [0.007]*** [0.007]*** [0.007]056]*** [0.056]*** [0.056]*** [0.056]*** [0.006]*** [0.006]*** [0.006]*** [0.006]105]*** [0.105]*** [0.111]*** [0.109]*** [0.012]*** [0.011]*** [0.012]*** [0.012]059]*** [0.059]*** [0.059]*** [0.059]*** [0.008]*** [0.008]*** [0.008]*** [0.008]223]*** [0.224]*** [0.230]*** [0.227]*** [0.024]*** [0.024]*** [0.025]*** [0.027]brackets ; * significant at 10% ; ** significant at 5% ; *** significant at 1%Tab. 4 -Financial Constraints and the decision to export : Dynamic specifications brackets ; * significant at 10% ; ** significant at 5% ; *** significant at 1%

  brackets significant at 10% ; ** significant at 5% ; *** significant at 1%Tab. 6 -Financial constraints and the decision to start exporting brackets ; * significant at 10% ; ** significant at 5% ; *** significant at 1%

  brackets significant at 10% ; ** significant at 5% ; *** significant at 1%

  brackets significant at 10% ; ** significant at 5% ; *** significant at 1%

  brackets significant at 10% ; ** significant at 5% ; *** significant at 1%

  Table 2 presents descriptive statistics for different types of firms present in the dataset :

  18 Firms are allocated to one of the following 14 industrial sectors : Clothing and footwear ; Printing and publi-Expdum it = a 0 + a 1 Very small i(t-1) + a 2 Small i(t-1) + a 3 Medium i(t-1) + a 4 Large i(t-1) + a 5 W age i(t-1) + a 6 T F P i(t-1) + a 7 Subsidiaries i+ a 8 F inconst i(t-1) + industry + time + it (2)where the subscript i indexes firms and t, time. Expdum is a dummy variable equal to 1 if firm i exported in year t, and 0 otherwise. V erysmall (respectively Small to Large) is a dummy variable equal to 1 if the firm i's real assets in t are in the first quintile (respectively in the second to the fifth quintile. Very large is the omitted category. W age is equal to the ratio of the firm's total wage bill to the number of hour worked, T F P is our index of relative productivity (see, Subsection 3.3). Subsidiaries is a dummy variable equal to 1 if the firm has subsidiaries, and 0 otherwise. F inconst denotes alternatively each of our four measures of financial constraints :

shing ; Pharmaceuticals ; House equipment and furnishings ; Automobile ; Transportation machinery ; Machinery and mechanical equipment ; Electrical and electronic equipment ; Mineral industries ; Textile ; Wood and paper ; Chemicals, Metallurgy, Iron and Steel ; Electric and Electronic components

  here]

				Tab. 1 -Correlations between Financial Constraints indexes
				Pearson's r and Spearman Rho Correlation Coefficient
					Liquidity ratio Leverage ratio Score A Score B
	Tab. 3 -Financial Constraints and the decision to export : Static specifications	Random-Effects Probit Fixed-Effects Linear Probability Model	(1)	Liquidity ratio Leverage ratio Score A Score B Numbers in italics denote Spearman rho correlation coefficient 1 -0,90 0,50 0,45 -0,92 1 -0,55 -0,49 0,46 -0,46 1 0,90 0,41 -0,41 0,90 1 Tab. 2 -Descriptive statistics Continuous Exporters variable obs mean std. dev. min max Liquidity ratio 43858 0,324 0,275 -3,66 1,00 Leverage ratio 43858 0,598 0,377 0 9,01 Score A 43858 5,747 1,776 0 10 Score B 43858 6,925 2,410 0 10 log Employ 43858 11,573 0,812 10,32 14,88 log TFP 43858 0,034 0,155 -1,42 1,16 Export Starters variable obs mean std. dev. min max Liquidity ratio 7113 0,271 0,276 -1,75 0,98 Leverage ratio 7113 0,670 0,392 0 7,18 Score A 7113 5,460 1,836 0 10 Score B 7113 6,598 2,551 0 10 log Employ 7113 11,198 0,626 10,32 17,47 log TFP 7113 0,021 0,163 -1,18 1,29 Never Exporters
				variable	obs	mean std. dev.	min	max
				Liquidity ratio 10583	0,254	0,312	-1,98	1
				Leverage ratio 10583	0,706	0,480	0	7,64
				Score A	10583	5,333	1,853	0	10
				Score B	10583	6,520	2,551	0	10
				log Employ	10583 11,082	0,610 10,32 14,94
				log TFP	10583	0,012	0,175	-1,60	1,53

  Tab. 5 -Self-selection into exporting by less constrained firms

		t-3, t
	Score B
		t-1, t
		t-3, t
	Score A
		t-1, t
	Leverage ratio	t-1, t t-3, t
	Liquidity ratio	t-1, t t-3, t

  Tab. 7 -Ex-post effects (in levels)

		t, t+3
	Score B
		t, t+1
		t, t+3
	Score A
		t, t+1
	Leverage ratio	t, t+1 t, t+3
	Liquidity ratio	t, t+1 t, t+3

  Tab. 8 -Measuring the Ex-post effects (growth rates)

		t, t+3
	Score B
		t, t+1
		t, t+3
	Score A
		t, t+1
	Leverage ratio	t, t+1 t, t+3
	Liquidity ratio	t, t+1 t, t+3

  Tab. 10 -Ex-post effects (in levels) : results excluding switchers

		t, t+3
	Score B
		t, t+1
		t, t+3
	Score A
		t, t+1
	Leverage ratio	t, t+1 t, t+3
	Liquidity ratio	t, t+1 t, t+3

The assumption that entry into foreign markets involves large sunk costs is supported by an expanding empirical literature (see, amon others,(Bernard and Wagner,

[START_REF] Tybout | Plant-and firm-level evidence on "new" trade theories[END_REF][START_REF] Das | Market entry costs, producer heterogeneity, and export dynamics[END_REF][START_REF] Tybout | Plant-and firm-level evidence on "new" trade theories[END_REF][START_REF] Bellone | The u-shaped productivity dynamics of french exporters[END_REF]

This is the maximum amount of resources that a firm can devote to self-financing, and corresponds to the French capacité d'autofinancement.

To account for the presence of outliers we trim the top and bottom 0.5% observations for each variable.

We have tried also other ways to combine the information, with identical results. Additional details are available upon request.

See Bellone et al. (2008) for more details on the method and a full description of the variables.

In this regression, both the continuous exporters and the switchers are excluded

Note that, when the test is performed on the entire period, it is as if continuous exporters were compared to their never exporting counterparts.

Acknowledgments

The authors blame each other for any remaining mistake. They nevertheless agree on the need to thank Sylvain Barde, Jean-Luc Gaffard, Sarah Guillou, and Evens Salies for useful comments and discussions.

Références

Altman, E. (1968), 'Financial ratios, discriminant analysis and the prediction of corporate bankruptcy', The Journal of Finance 23(4), 589-609.

in terms of its access to external finance that help it afford the costs of entry into exporting at time t, and it continues experiencing such favorable shocks after the time t of entry. In cases like that, how do we identify expost benefits from exogenous positive shocks that have nothing to do with exposure to exporting ? This difficulty lies at the heart of the debate on the presence of Learning-by-exporting effects as recently reviewed by [START_REF] Isgut | Learning-by-exporting effects : Are they for real ?[END_REF].