Frédéric Pedrinis
email: frederic.pedrinis@liris.cnrs.fr

Gilles Gesquière
email: gilles.gesquiere@liris.cnrs.fr

Reconstructing 3D building models with the 2D cadastre for semantic enhancement

Keywords: 3D Virtual City, cadastre, CityGML, semantic information

Virtual city models are increasingly used in urban land management processes, which involve the use of different sources of spatial information. This heterogeneous data is, however, often complementary and it may be necessary to give the possibility to join information provided by different sources. This paper presents a method to enhance 3D buildings by using usual 2D vectorial polygon database. These polygons may represent districts, building footprints, or any segmentation of the urban area that adds information to the city model. The enhancement consists in using this polygon database to split the 3D buildings into a set of city objects where each element possesses a 3D geometry and the semantic information of the polygon it is linked to. In this paper, for an illustration purpose, we will present how to create this link between 3D buildings and the cadastre map, in order to create a set of semantically rich 3D building models.

Introduction

Many cities possess a virtual 3D model representing their territory. They have at their disposal various methods to build their virtual double, depending on the available data and the desired model. Therefore, international standards are currently being developed to manage these 3D city models, like the CityGML standard1 created in 2008 by the Open Geospatial Consortium2 [START_REF] Gröger | OpenGIS City Geography Markup Language (CityGML) Encoding Standard, Version 1.0.0[END_REF][START_REF] Kolbe | Representing and Exchanging 3D City Models with CityGML[END_REF]. It is a format that allows the complete description of a building, including 5 different Levels of Details (LoD) and semantic information, but these are rarely present in a newly generated 3D model. 3D urban model construction processes mainly use imagery and/ or LiDAR scans to create the 3D geometries of the city (Musialski et al. 2012). They focus on the elaboration of correct 3D geometries in order to propose a visually convincing representation of the city. The semantic richness of buildings defined in the 3D geometries is not really discussed, and these objects can't be directly connected to urban databases.

However, other representations of the city can contain the information needed to complete the database. 2D polygonal databases, like for instance the cadastre map, can be used to generate this enhancement of a 3D city model. Such a 2D polygonal database describes an urban area and provides semantic information for each of its elements represented by a polygon. An example would be a partition of the city into polygonal zones according to some characteristics like the buildings date of construction or the average age of their inhabitants. More generally, the method could be used with every 2D database providing a partition relevant to city objects.

In this paper, we choose to focus on the use of cadastre maps to enhance the 3D buildings. In addition to a precise notion of buildings, the cadastre provides semantic information and can grant access to non-georeferenced databases. For example, we can access to the date of construction of a building, its owner's name, its number of housings, or to collect the result of a thermal simulation attached to cadastral buildings. This is why we want to develop a method to link a given 3D building model with the corresponding cadastral polygons. This link is used to create a new model containing, for each building initially defined in the cadastre, a 3D geometry computed from the initial 3D model. The union of these buildings would thus have a 3D model similar to the initial one, and a possible connection with all databases accessible from the cadastre. Figure 1 illustrates this possibility. The cadastral ID provides an access to semantic information. Thanks to our enhancement process described in this paper, the link between the cadastre and the initial 3D model of buildings transfers this accessibility to the resulting model. Two different ways to generate the link between the cadastre, or any other polygons database, and 3D models can be identified. The first one is to directly involve the 2D polygons in the construction process of 3D geometries, as in Durupt and Taillander (2006), [START_REF] Vallet | Building footprint database improvement for 3D reconstruction: A split and merge approach and its evaluation[END_REF][START_REF] Agugiaro | From sub-optimal datasets to a CityGML-compliant 3D city model: experiences from Trento, Italy[END_REF], who used cadastral data to design a robust 3D reconstruction of buildings. The second way consists in a post-process intervention on the geometries in order to associate them to the needed semantic information. In this case, we don't need a process to build a 3D model from raw data, as we can just use an existing one. [START_REF] Ross | Enhancing 3d city models with heterogeneous spatial information: Towards 3d land information systems[END_REF] propose to add information to 3D city models to create complex 3D Land Information Systems. Among the concerned data, they choose to automatically add attribute information extracted from the cadastre map to the 3D geometries of buildings. The authors do not really describe how this is processed. However, such additions should require a certain overlap between the 3D geometry and the cadastre to be relevant, which is not the case in our datasets. For each object initially called "building" in the 3D model (Figure 2, top-left), multiple cadastral objects, which also represent "buildings" according to their definition (Figure 2, bottom-left), can match. We have to decide which cadastral object may be linked to the 3D geometry, and which should be ignored. The proposed solution is to split the geometry to provide a new 3D model for each cadastral footprint (Figure 2, right). The geometry and the texture coordinates are extracted from the initial 3D buildings.

Fig. 2.

A single building from a 3D city model (top-left) and the cadastral buildings of the same area (bottom-left) are linked; a split 3D model according to the cadastre is generated by our method (right). A building is picked (highlighted in red), and some other ones are hidden (yellow polygons on the bottom-left). Each of these buildings has a set of semantic information collected thanks to the cadastre.

Our tests are made on the data of the city of Lyon (France), which are available on the Lyon Data website3 . We implemented our method on the software 3D-Use developed by our team4 .

In this paper, we will first present an overview of our method (Section 2). Then, we will present how we create the link between the two datasets with 2D processes (Section 3), before involving the 3D to get a better result (Section 4). The paper continues with the generation process of the new 3D model, which contains the semantic information stored in the cadastre (Section 5). We will then propose some tests and discussions (Section 6) before concluding and presenting our future works (Section 7).

Overview of our method

To illustrate our method, we will use two data sets. This first one is a CityGML file containing 3D models of buildings in LoD2 (Figure 3, left). The second one is the French Cadastre which is a 2D vectorial polygons database (Figure 3, right). Since the buildings' definition is conveyed by the cadastral polygons, we want to modify these polygons so that they completely cover the surface represented by the footprints of the input 3D models of buildings. Since buildings are modelled in LoD2, covering their footprints means being able to entirely assign their geometry to cadastral polygons and to regenerate 3D geometries, as we will see in Section 5. However, if we look closely at the pictures of Figure 3, we can already identify some inconsistencies between the footprints, such as lacks of courtyards or some differences for small pieces of buildings. This reflects that the two databases do not properly overlap.

We illustrate this observation on the left picture of Figure 4, which is a focus on the rectangular selection of the right picture of Figure 3. These differences may have several explanations that are listed below. The first one is linked to the precision that is not the same for the two datasets. A second set of difference is due to the acquisition date. Third, these acquisition methods are simply not comparable. For example, in CityGML LoD2 models of buildings a footprint is defined by the roof shape. As we can see on the right picture of Figure 4, there are common cases of buildings where such footprints are irrelevant, when there is an offset between the wall and the roof border, and the cadastre logically does not use them. The footprints are wider than the footprint generated from the real walls that the cadastre probably use. Even if the cadastre footprint logically represents the more realistic representation, our objective here is to split the LoD2 3D geometry and link it with cadastral areas.

Fig. 4. Inconsistencies between footprints of 3D buildings (blue) and cadastral polygons (red).

The exact process of generating 3D geometries from a footprint and a 3D model will be presented in Section 5. If we use this process on the raw data of the cadastre, some wall and roof polygons of the 3D model will not be assigned to the newly generated buildings. More generally, the 3D geometry will be unpredictable, and probably visually unrealistic. We would only obtain a cut of the 3D geometry with an unrelated mask defined by the cadastre, and a part of this geometry would be lost. Figure 5 illustrates this problem: the cut process without any preparation of the footprints is presented on the left, while the initial model is on the right. The lost part of the 3D geometry is illustrated in green, wall and roof polygons that are not entirely on the area defined by the cadastre cannot be naïvely assigned to a building in the final 3D model. In our dataset based on Lyon CityGML files, we have calculated that the proportion of 3D models, in terms of superficies, that are not covered by the cadastre is about 8 % of the total building superficies. If we cut only with the raw cadastre, we would thus lose a significant part of the 3D model, especially as these losses mainly concern the external envelope of the buildings, which is the most visible part mapped with texture.

Another problem that may appear with a raw cut is the gap between the visible separations of two buildings on the 3D model and the corresponding split defined in the cadastre. A case is illustrated on Figure 6. A cut is generated with the unchanged footprints of the cadastre (left). The cut generated by our method, which adapt the footprints according to the 3D geometry, is presented on the right and is visually more satisfying. This means that at least one of the model has to be modified. Since we don't necessary have the data to construct a new 3D textured model, we focus on adapting the cadastral footprints to the initial 3D geometry, and to keep a link between these new polygons and the original cadastre. These problems have been identified in [START_REF] Pedrinis | Change Detection of Cities[END_REF] and a first method has been proposed to solve this pairing between the cadastre and 3D buildings in order to provide a better detection of changes between two 3D models available at two different dates. However, this first tentative is not enough to solve all the problems presented in this section. A global overview of our method is proposed in Figure 7; it also introduces the notations used in the following of this paper. G is a set of 3D geometries that are used to generate building's footprints by projecting the roof polygons on the ground (FP1).

On the other side, the set of polygons FP2 represents the footprints according to the cadastre. Each footprint may have semantic information Sd. The two sets of footprints are merged to generate a new one, FP3, defining the cadastral footprints from FP2 that are expanded to cover the entire surface of FP1. This step corrects the error shown in Figure 5. For that presented in Figure 6, G is used to modify FP3 by adapting footprints to the related 3D geometry. This new set of footprints is called FP4. It is then possible to generate a new 3D model G2 by cutting the 3D polygons of G according to polygons of FP4. A natural link is now available and G2 can access to the semantic data Sd initially proposed by the cadastre.

Merging footprints from the 3D and cadastral models

The previous section has pointed out the need to adapt cadastral polygons to the footprints generated from the 3D models of buildings, in order to be able to use them for the generation of the 3D geometries of new buildings. We thus have two sets of polygons FP1 and FP2 and we want to generate a new set of polygons FP3 that will contain footprints of FP2 modified to cover the entire surface of polygons from FP1. For the example represented on the right picture of Figure 4, this means that the red polygons will entirely cover the blue one. To achieve this, the difference between FP1 and FP2 is computed to produces a set of polygons Diff. These areas correspond to the surface of FP1 that was not initially covered by FP2 (presented in green in Figure 8). These polygons Diff represent the area that needs to be filled by the expansion of the polygons of FP2. However, this expansion has to be controlled: the result has to be visually convincing considering that it will define the future division for 3D models of buildings. Each Diff polygon is split according to its neighbouring polygons from FP2, in order to assign the best possible shape to each of them.

Points on Diff that are on the boundary of two cadastral footprints are detected (red points of Figure 8). These points are used to split Diff into distinct polygons, which will be assigned to the concerned cadastral polygons. The resulting footprints need to be visually credible. The more convincing line passing through P that extends the border line must be chosen to split the Diff in two parts. To reach this goal, P is projected on other edges; the best projection P' according to parameters of distance or angles. The angles between [PP'] and the two neighbouring edges of P should be close and the [PP'] segment should be as short as possible. In our implementation, we chose the projection with the shortest segment, except if the two angles are too different. In the example of Figure 9, P2 and P3 are eliminated by P' and P1 due to their smaller distance to P. P1 is rejected because the angles formed with the neighbouring edges of P are too different. P' is thus chosen and the line defined by P and P' will be used to split Diff into two resulting polygons. This process applied on the selected area of Figure 8 provides the result presented in Figure 10. The last step of this process consists in assigning each sub-polygon (blue ones in Figure 10) to the nearest cadastral footprint (beige polygons) to expand it. The chosen corresponding footprint is the one with which the polygon shares the longest border.

Correction of generated footprints by using 3D geometry

This set of polygons FP3 allows to generate a 3D model, with the process explained in Section 5, since these footprints now cover the entire surface of FP1. However, as we can see in Figure 12 (left), which is a focus on the orange selected area of Figure 11, the result would not be visually satisfactory. Initially, the footprints generated from CityGML buildings only take into account the (x,y) coordinates of roof polygons (Figure 12, middle). This means that 3D discontinuities of the roof, as seen on the Figure 12 (left), do not interfere in the choice of splitting edge between two new footprints. In order to prepare better 3D models, we have to use this information to propose a new version of footprints that will consider the 3D shape of the future generated buildings. The footprints of FP3 is split according to the roof discontinuities: if a wall of the input 3D model crosses a footprint of FP3, it must be split along the 2D line representing this wall (Figure 12, right). The split results in a set of polygons for each element of FP3. These polygons are represented on Figure 13. Each of them keeps a link to its original footprint of FP3. Among these polygons, those that are characteristics of visual inconsistencies are the small or elongated ones: they represent footprints spilling over their neighbours. They are represented in light green in Figure 13 and we will call them Sp. We need to determine which of these polygons must be reallocated to other footprints in order to correct the visual inconsistencies.

The polygons are added to Sp if they fall into one of these 3 categories: the very small polygons, the small and non-compact polygons, and the elongated ones. Two parameters are proposed to detect the concerned polygons: the area and the Gravelius Compactness Coefficient (Kg) of a polygon. The second parameter Kg for a polygon P is defined by 𝐾𝑔(𝑃) = 𝑃𝑒𝑟𝑖𝑚𝑒𝑡𝑒𝑟(𝑃)/(2 * √𝜋 * 𝐴𝑟𝑒𝑎(𝑃)). This coefficient is initially used to analyse watersheds [START_REF] Pareta | Quantitative morphometric analysis of a watershed of Yamuna basin, India using ASTER (DEM) data and GIS[END_REF]. Kg is equal to 1 if P is a circle and is inversely proportional to its compactness (Figure 14). This parameter is used to detect elongated polygons.

Fig. 13. Split polygons according to 3D discontinuities. Light green ones have been selected for their elongated shape or small area. Each of the polygons Sp is then compared to the neighbouring footprints of FP3. The polygon is reallocated to the footprint with which it shares the longest continuous border in the 3D model. If no borders are found, the polygon is left to its original footprint.

For the illustration presented in Figure 12, we detect on the left of Figure 15 the elongated polygons A and B (green polygons). We test them with the two cadastral foot-prints 1 and 2 (purple polygons). A and 1 (resp. B and 2) are considered as the better neighbours. We can see on the middle of Figure 15 the two resulting footprints and, on the right, the resulting 3D models. The final version of the buildings footprints FP4 is presented in Figure 16. This set of polygons can be used now to generate the 3D model.

Fig. 16.

Final version of footprints FP4 that will be used to generate 3D models of buildings.

Creation of the new 3D city model

Each footprint stored in FP4 represents a building. We want to create a new 3D city model containing all these buildings, so we have to generate 3D geometries G2 for each of them. Since we want to generate a 3D model for each element of FP4, we split the 3D polygons of G accordingly to the footprints of FP4, before assigning the resulting polygons to the concerned footprints in the new CityGML buildings. Textures coordinates are then computed for each building by using those stored in the input 3D model. However, existing walls are not enough if we want an independent and complete building in the final CityGML file: we have to generate hidden walls to close each building. Otherwise, we would have holes in the geometry when a created building would be displayed alone. We thus detect edges of FP4 that represent border between two footprints (green edges in Figure 17), and we create walls or extend existing walls at their position. For the example of Figure 15, we can see a preexisting wall on the border between footprints 1 and 2. This wall has to be extended to the ground to generate two closed geometries. These generated walls do not have textures because they were initially hidden, so they are displayed with a default colour (here white) and can be viewed by hiding their neighbours (Figure 2, right).

Since polygons of FP4 are originally extracted from cadastral footprints, the semantic related information can be assigned to the corresponding generated 3D model (Figure 18). For instance, here, data describing the construction and modification dates, the surface and the perimeter are available.

Performance and discussion

We have tested our method on two districts of the city of Lyon (France). The result on the first district is presented Figure 19. Table 1 gives some performances data generated with a computer on Windows 7 with an I7-4790K @ 4.00GHz CPU. We can see on Table 1 that the number of buildings logically increases after the process; however it does not mean that all buildings from the initial CityGML file or those from the cadastre have been kept. It is possible that some footprints did not find any equivalent in the other database. This information can be exported by our software 3D-Use since it may be useful in a validation process of the cadastre for example: these differences can be representative of an out of date cadastre. In our case, this may signify that our process should then require a human intervention to verify the corresponding buildings, on the field or with another model of the city. After discussing with urban operators who manually realize a similar geometry cut, we do think it is anyway necessary to keep a human validation step in our global enhancement process. Some cases lead to disagreements even between different human operators, so changes should be possible on the created model by following the process depicted in Figure 20. FP4 are used to generate G2 but an expert has the possibility to detect inconsistencies in the 3D model cut, eventually guided by computed indicators based on 3D analysis processes. Concerned footprints are then exported to allow modify manual correction by the expert before reinserting them in the set of footprints used to generate a new version of the buildings 3D model. This process can be repeated several time and stopped by the expert or when the possible inconsistencies become under a given threshold.

Fig. 20. Semi-automatic validation and correction of the computed footprints

Decomposing the method in two parts also gives the possibility to use an extra set of polygons in order to cut 3D geometry. We illustrate this possibility in Figure 21: a set of random polygons (in blue) are used to cut the initial building. In this way, the second part of our method could be used in several other applications like a tiling process for example, or for any method that requires to group buildings accordingly to 2D shapes, which could eventually contain semantic information.

Conclusion and future works

Nowadays, a large amount of 3D city models are available. The accuracy of reconstruction processes of these models has been increased but the linked semantic is often poor and it may be difficult for a user to link the needed information with these 3D models. On the other side, a large diversity of semantic information linked to 2D models like the cadastre is available. In this paper we propose a method to link these two kinds of data in order to enhance dedicated data linked to 3D buildings. Since these two models have no reason to be correctly fitted, some processes are required to pair their representation and to generate a merging model. We have proposed corrections on the 2D polygons to make them split the entire 3D geometry and to get convincing new 3D models of buildings. The two datasets are thus closely related. The 3D geometry is involved in the description of the footprints based on the 2D database, while each of them is then used to cut the 3D model and generate a new 3D building. This link between two datasets can also be used to compare two models representing the city at two different dates (inducing a real enhancement of the method proposed in [START_REF] Pedrinis | Change Detection of Cities[END_REF]). It also allows to evaluate one of the model by a second which is deemed true. The presented processes are not necessarily sufficient to generate a city model wholly convincing. They may need to be followed by a semi-automatic procedure involving an urban expert to produce a better 3D model of the city.

The presented method has been presented to experts. The feedbacks are very positive.

Our approach could provide a good alternative to their actual time consuming methods.

Nevertheless, some works remain to be done, in particular to propose a semiautomatic loop for a guided correction by experts in our software. For example, even if the process that automatically corrects error such as 3D inconsistencies in the resulting model can be improved, it should be more relevant to begin by just proposing a detection process of these errors to help the expert correction task. For example, we may propose an evaluation of our results by computing matching indicators between a cadastral footprint and the corresponding 3D geometry.

The method presented in this paper was developed with LoD2 buildings according to the CityGML definition, it may also be necessary to extend it to more precise models.

Fig. 1 .

 1 Fig. 1. The link created between 3D buildings and the cadastre generates a new 3D model composed of precise buildings that can access to external databases with their cadastral ID.

Fig. 3 .

 3 Fig. 3. CityGML buildings are on the left, cadastral buildings on the right. The rectangular selection on the cadastre corresponds to a zoom used in Figure 4.

Fig. 5 .

 5 Fig. 5. Cut of the 3D model according to the cadastre without correction will lead to have missing parts (left). The lost part of roof and wall polygons are represented in green on the initial model (right).

Fig. 6 .

 6 Fig. 6. Left image corresponds to a rough cut with the unmodified cadastral footprints. The right one is generated with the corrected footprint that takes into account the 3D geometry of the buildings models.

Fig. 7 .

 7 Fig. 7. Presentation of the main steps of our method. The sets of 2D polygons are in green, while the 3D geometries are in red.

Fig. 8 .

 8 Fig. 8. Difference between FP1 and FP2 (beige polygons). The resulting polygons Diff are represented in green. Red points that are on the boundary of two cadastral footprints of FP2 are then detected.

Fig. 9 .

 9 Fig. 9. Orthogonal projections of point P from polygon Diff (green) on its other edges gives points P1, P2, P' and P3. Due to angle and distance criteria, P' is chosen. Beige polygons are cadastral footprints that were used to detect P.

Fig. 10 .Fig. 11 .

 1011 Fig. 10. Diff is split into blue polygons, which are assigned separately to their nearest cadastral polygon (beige).

Fig. 12 .

 12 Fig. 12. On the left is shown the corresponding 3D cut of the footprints (middle), which are taken from the selected area (orange rectangle) of Figure 11. The expected cut corresponding to the wall of the 3D model is represented on blue (right).

Fig. 14 .

 14 Fig. 14. Some values of the Gravelius Compactness Coefficient (Kg).

Fig. 15 .

 15 Fig. 15. Elongated polygons A and B are detected (left) and are respectively merged to footprints 1 and 2 (middle) in order to propose two distinct footprints that will give a visually satisfying 3D geometry (right).

Fig. 17 .

 17 Fig. 17. Detection of missing walls for generated buildings.

Fig. 18 .

 18 Fig. 18. Semantic information extracted from a footprint and linked to a 3D building.

Fig. 21 .

 21 Fig. 21. Cut of a 3D building (on the right) with some polygons (blue ones, on the left).

Table 1 .

 1 Performance of enhancing CityGML for two districts of the city of Lyon. Each building of the output CityGML file corresponds to a cadastral footprint. Enhanced 3D model describing the first district of the city of Lyon. A multi-selection of generated buildings is highlighted in red.

	District (superficy)	Number of Buildings File size Input CityGML file	Enhancement process Time	Nb of Buildings File size Output CityGML file
	Lyon 01 (1,5 Km²)	409	110 Mb	1197 s (20 min)	2640	132 Mb
	Lyon 04 (2,9 Km²)	999	118 Mb	1461 s (24 min)	4339	148 Mb

-Fig. 19.

http://www.citygml.org/

http://www.opengeospatial.org/

http://data.grandlyon.com/

http://liris.cnrs.fr/vcity/wiki/doku.php

Acknowledgement

This work was performed within the BQI program of Université Lyon 1. This work was also supported by the LABEX IMU (ANR-10-LABX-0088) of Université de Lyon, within the program "Investissements d'Avenir" (ANR-11-IDEX-0007) operated by the French National Research Agency (ANR). Data are provided by "Lyon Métropole". The authors would like to thanks the DINSI team of Lyon Métropole for their valued feedbacks during this collaboration.


Alain Bonnafous Professeur

La question de savoir si la recherche en économie des transports produit les connaissances nécessaires pour que soient convenablement éclairées les décisions des acteurs est une bonne question. Si la réponse est non, cela désigne une première carence dont on voit bien les inconvénients quant à l'efficacité de la décision. Cette première situation et les explications que l'on peut en entrevoir seront examinées dans un premier temps (sections 1 et 2).

Pour que la réponse soit oui, quelques conditions sont requises qui seront examinées dans un second temps (section 3). A supposer que soit acquise cette situation, dans laquelle les besoins de connaissance de la décision sont convenablement satisfaits par les productions de la recherche, il reste à savoir si la sphère de la décision reçoit bien les messages qu'émettent les milieux de la recherche. En cas de réponse négative, il convient de s'interroger sur les raisons de ce déficit de communication et sur les moyens de le combler (section 4).

L'UTILITÉ SOCIALE ET L'UTILITÉ ACADÉMIQUE

L'une des manières de caractériser les situations que nous avons esquissées consiste à situer les productions de la recherche par rapport à deux critères qui peuvent être corrélés ou, au contraire, systématiquement opposés selon les pays, les époques ou même les thèmes concernés : un critère d'utilité sociale et un critère d'utilité académique. Le premier est supposé représenter la satisfaction des besoins de connaissance et d'expertise de la société ; le second, les évaluations des milieux scientifiques. Pour la commodité du raisonnement, nous supposerons également que ces critères sont mesurables et que tous les produits de la recherche peuvent être ainsi situés par rapport aux deux axes représentatifs de l'utilité sociale et de l'utilité académique.

Observons, en premier lieu, qu'il y a quelques raisons pour que la recherche soit écartelée entre les deux critères. En effet, l'utilité sociale d'une investigation tient d'abord à son aptitude à répondre aux questions imposées par les circonstances ou par l'imminence d'une décision. Un bon niveau d'utilité sociale consistera, par exemple, à construire un modèle de prévision aussi consistant que possible et, pour cela, à affecter des moyens importants à la production et au traitement des données. En revanche, la formalisation du modèle sera limitée au strict nécessaire.

Pour un même objet, un bon niveau d'utilité académique correspond à l'élaboration d'un modèle plus sophistiqué et qui doit être démarqué des outils existants, du moins dans sa formalisation. Son utilité académique tenant d'abord à son aptitude à être bien évalué par les milieux universitaires, son opérationalité devient un critère secondaire par rapport à ses qualités formelles : plutôt que de confronter le modèle à l'observation, c'est-à-dire aux données disponibles, il importe de le situer par rapport à "l'état de l'art", c'est-à-dire à ce que les auteurs reconnus ont établi sur le sujet. D'une certaine manière, c'est un effort théorique qui se substitue à l'effort empirique.

Pour une quantité déterminée de moyens, cette substituabilité entre les critères s'exprime par une silhouette de courbe représentative des différentes sortes d'investigations telle que celle de la Figure 1.

Figure 1. Des qualités substituables

Cette configuration n'interdit pas une ouverture du monde de la recherche à la demande sociale. Un institut universitaire peut, par exemple, partager ses activités entre des recherches donnant lieu à des publications scientifiques et des travaux contractuels demandés et financés par le monde de la décision. Les premières stimulent l'effort théorique et, accessoirement, le périple professionnel des chercheurs dans le monde académique. Les seconds ont le mérite d'attirer les chercheurs vers des questions vives qui préoccupent la société et, accessoirement, apportent des capacités de financement sans lesquelles les programmes de recherche seraient considérablement bridés dès l'instant qu'ils requièrent des productions et des traitements de données spécifiques.

Utilité sociale

Utilité académique

Réciproquement, un bureau d'étude doit, certes, financer l'intégralité de ses coûts par des contrats d'études, mais il a tout intérêt à consacrer une part de ses activités à une veille scientifique et à la production de connaissances théoriques, sauf à courir le risque de confiner ses activités dans des tâches répétitives et de ne mobiliser que des méthodologies destinées à devenir obsolètes.

En explorant l'axe de l'utilité sociale, le monde académique se donne les moyens d'une indispensable connaissance empirique. En explorant l'axe de l'utilité académique, les bureaux d'étude se donnent les moyens d'un indispensable renouvellement théorique. Ainsi, leurs travaux sont-ils appelés à être confrontés, aussi bien dans le langage des questions concrètes que pose le monde de la décision, que dans celui des publications scientifiques, chacun des producteurs contribuant à sa manière à l'effort de traduction entre les deux "langues".

Cependant, cette mobilité le long de la courbe qui exprime la substituabilité entre les deux critères ne correspond pas nécessairement à une dynamique stable. Les deux métiers de la recherche et de l'étude n'ont pas, en somme, les mêmes clientèles, mais chacun a besoin d'aller rechercher celle de l'autre pour assurer son développement. Deux attitudes sont alors possibles selon que cette double contestabilité est vécue comme illicite, ce qui conduit à un scénario de méfiance, ou selon qu'elle est acceptée comme une chance, ce qui conduit à un scénario d'émulation.

LE SCÉNARIO DE MÉFIANCE

La pathologie majeure de cette dynamique de confrontation présente un symptôme flagrant : chacun des acteurs de la recherche et de la décision n'agit que sur le "marché" qui le concerne, ne serait-ce que parce qu'il ignore ce qui peut se passer sur l'autre. Les acteurs de la demande sont les premiers à s'enfermer dans leurs sphères respectives.

Dans la sphère académique, il s'agit des évaluateurs qui ont en charge la sélection des articles des revues reconnues, de ceux qui composent les jurys de thèse ou élisent les jeunes collègues, ou encore de ceux qui allouent les crédits publics aux équipes de recherche, les mêmes personnes étant fréquemment appelées à jouer tous ces rôles à la fois. Elles tiennent ce pouvoir d'une réputation d'exigence qu'il s'agit d'entretenir en rejetant tout ce qui ne peut être reconnu d'un haut niveau académique. Cela conduit à une dérive bien connue dans les sciences économiques pour avoir suscité, dès le début des années 70, de saines réactions de la part de ceux qui avaient plus de légitimité que d'autres à les faire entendre.

C'est par exemple O. Morgenstern qui, après un exposé des difficultés inhérentes au traitement statistique en économie, observe que "face à ces difficultés, il n'est pas étonnant que les économètres trouvent plus commode d'élaborer des méthodes abstraites et raffinées que de les mettre en pratique"

1 . C'est encore W. Leontief qui n'est pas surpris que beaucoup "paraissent tout à fait satisfaits d'une situation où ils peuvent faire étalage de leurs prouesses (...) en construisant des modèles mathématiques de plus en plus complexes et en mettant au point des méthodes statistiques déductives de plus en plus raffinées sans jamais se lancer dans la recherche empirique" [START_REF] Leontief | Theorical Assomptions and Nonobserved Facts[END_REF] .

Le plus grave de la situation ainsi dénoncée tient à sa capacité à se reproduire : dans ce monde académique là, les critères de sélection professionnelle font que les futurs évaluateurs auront toutes les raisons d'aggraver la tendance de ceux qui les ont choisis car l'univers des données empiriques et de l'observation leur sera plus étranger encore. Pour ne pas avoir à l'affronter, il n'est alors que de le mépriser et, pour mieux le mépriser, il n'est qu'à en dénoncer la médiocrité. Le vocabulaire est prêt pour cela : la recherche d'un côté (le noble) et les études de l'autre (le laborieux).

Sur ce marché académique, l'auteur-offreur, pour être publié, recruté, promu ou aidé de crédits publics, devra donc produire "les prouesses" formelles qu'exige la demande. Il verra son offre rejetée, si elle n'est pas bien située sur l'échelle académique ainsi établie, quelle que soit par ailleurs l'utilité sociale de ses résultats. Dans une pathologie extrême, cette utilité sociale peut même devenir un handicap.

Sur l'autre marché, celui des connaissances utiles à la décision, la demande est ainsi complètement dissuadée de s'adresser au monde de la recherche. Il est réputé ne produire que des énoncés théoriques dont les rapports aux réalités sont bien lointains. Des énoncés que le décideur ne peut lire qu'en souffrant sans comprendre alors que sa demande légitime est de comprendre sans souffrir.

La demande du côté de la décision ne peut alors que s'appuyer sur ses propres fournisseurs. Ce sont, en particulier, des bureaux d'étude spécialisés sur des missions les plus demandées. Pour assurer le développement des outils méthodologiques, les décideurs peuvent compter sur les capacités d'innovation des bureaux d'étude les mieux structurés ou, à défaut, susciter leur propre système d'offre d'investigation. C'est ainsi qu'ont pu se développer d'importants services d'étude et de recherche auprès des administrations centrales ou au sein de grandes entreprises nationales. Les produits de leurs recherches sont appréciés à l'aune de leur efficacité opérationnelle et peu diffusés dans les publications du monde scientifique. Le seraient-ils que cette diffusion serait ignorée des acteurs de la décision en raison de la culture de méfiance qui s'instaure entre les deux marchés.

Ainsi, dans le champ des utilités sociales et académiques un no man's land apparaît, qui correspond à la zone de publications qui ne sont reconnues par aucun des deux marchés, comme schématisé sur la Figure 2.

Zone non reconnue

Cette situation est évidemment peu propice à l'efficacité de l'ensemble : privé de la dialectique du livre et du terrain, le monde académique se complaît dans des productions dont seule l'esthétique formelle peut être appréciée ; privé du fruit des controverses théoriques, le monde de la décision doit se contenter d'instruments faiblement renouvelés. Tout le contraire, en somme de ce qui peut se passer dans un scénario d'émulation.

LE SCÉNARIO D'ÉMULATION

On aura compris que le précédent scénario repose sur des hypothèses "anthropologiques" relatives aux deux groupes d'acteurs. On peut évidemment décliner un jeu d'hypothèses très différentes qui implique une tout autre dynamique.

Ces différences nous semblent fondamentalement liées aux exigences du monde académique. Dès lors que celui-ci choisit de privilégier la scientificité des énoncés par rapport à la prouesse formelle, il ne peut que susciter la confrontation de la proposition théorique à l'observation et, donc, favoriser ce que W. Leontief désignait par "la recherche empirique". Il ne s'agit pas, bien entendu, de se contenter de mettre de l'ordre dans des données d'observation et de tomber dans l'illusion de "l'inductivisme", mais de construire le modèle théorique, quantitatif ou causal, par sa confrontation permanente avec ce que l'on peut observer de l'état des choses.

Sous cette exigence, élémentaire pour toute épistémologie contemporaine, la production et le traitement des données prennent toutes leur place et requièrent des moyens qui dépassent fréquemment ceux de la recherche académique. Les moyens complémentaires ne peuvent alors être trouvés que sur le marché de l'utilité sociale, là où les interrogations du chercheur peuvent rencontrer les besoins de connaissance du décideur. En acceptant cet enrichissement des recherches (au double sens du mot enrichissement), les évaluateurs du monde académique ne censurent plus les travaux à contenu empirique ou même à orientation opérationnelle. Dans le cas d'une évolution complète des esprits, l'utilité sociale est même intégrée dans les critères académiques d'évaluation. C'est ainsi que sera suscitée ce qu'il est convenu d'appeler une valorisation de la recherche.

Réciproquement, le marché opérationnel s'ouvrira d'autant mieux au monde de la recherche qu'il y récoltera des innovations conceptuelles ou méthodologies validées par leurs applications. Dans cette dynamique, les deux mondes ne peuvent qu'observer qu'ils ont des choses à s'enseigner mutuellement et ce que les recherches gagnent en pertinence, les travaux à vocation opérationnelle le récupèrent en puissance théorique. La substituabilité des critères devient ainsi complémentarité et la silhouette des productions des deux marchés s'inscrit alors dans des zones plus efficaces pour les deux critères, comme le représente la silhouette de la courbe sur la Figure 3. Ainsi que le suggère cette courbe, il reste, bien entendu, une place pour des travaux spécifiquement académiques ou pour des travaux à forte utilité sociale, mais sans grand intérêt pour le monde académique. Ces situations extrêmes peuvent être provisoires, car une recherche purement théorique peut avoir des retombées méthodologiques concrètes et rencontrer ainsi des domaines d'applicabilité, de même qu'une étude à stricte vocation opérationnelle peut susciter des résultats mal expliqués et poser ainsi des questions à la recherche ou encore fournir des bases de données inédites qui constituent autant de gisements pour des recherches innovantes. Contrairement à ce qui se passe dans le scénario de méfiance, ce n'est plus le double rejet, mais la curiosité réciproque qui fonde le système des relations entre les deux marchés qui s'enrichissent ainsi mutuellement. Faut-il encore, pour que le système trouve à la fois sa pleine efficacité opérationnelle et sa pleine efficacité scientifique, que la communication soit assurée entre les deux mondes.

UN PROBLÈME DE COMMUNICATION

Lorsque les obstacles liés à la culture de méfiance sont levés, l'enrichissement mutuel des problématiques de la décision et des problématiques scientifiques suppose, en effet, que l'information circule entre les deux versants. Cela pose un triple problème de diffusion des connaissances, de confrontation permanente et de mobilité professionnelle.

La diffusion des résultats de la recherche en économie des transports repose sur des moyens qui ne sont pas conçus pour toucher un vaste public. Les revues internationales à comité de lecture les mieux implantées et les plus reconnues dépassent difficilement les 1 000 abonnés. Lors de ses quatre dernières éditions, la Conférence Mondiale sur la Recherche en Transport n'a jamais dépassé les 1 200 participants. Ces ordres de grandeur montrent, s'il en était besoin, que le public intéressé par ce genre de production est à peu de chose près la population des producteurs eux-mêmes.

Utilité académique

Utilité sociale

Certes des efforts ont été faits pour que ces travaux soient accessibles, en particulier par la CEMT, avec la production d'une base documentaire d'une bonne efficacité et avec la recension des recherches en cours. En coordination avec la base de la CEMT, plusieurs centres universitaires ont développé leurs propres systèmes documentaires. Les principaux utilisateurs de ces bases sont, pour l'essentiel, les auteurs de travaux recensés et les étudiants mais, cependant, un nombre croissant d'usagers proviennent de bureaux d'étude prestataires de service pour le monde de la décision.

Cette forme de percolation des connaissances ne peut être considérée comme suffisante et il appartient au monde académique de faire un effort particulier en matière de diffusion de ses résultats. Beaucoup d'instituts de recherche font l'effort de produire une Newsletter régulière. Peu de chercheurs, en revanche, écrivent des ouvrages de vulgarisation susceptibles de rendre accessibles au plus grand nombre les principales démarches, y compris les plus récentes, relatives à un même thème. Cela tient à la fois à la difficulté et à la lourdeur de l'exercice et au fait que ce genre de publication est généralement peu pris en compte par les évaluateurs académiques.

Réciproquement, les productions spécifiquement commandées par les décideurs ne font que très rarement l'objet d'une publication ou même d'une recension documentaire. Cette production de "littérature grise" n'est, en effet, enregistrée dans les bases documentaires que lorsqu'elle parvient accidentellement dans les centres de recherche qui gèrent ces bases. C'est souvent à la faveur de recherches particulières menées méticuleusement que sont ainsi découverts des travaux à forte valeur ajoutée ou permettant de mieux comprendre les interrogations décisionnelles qui les ont suscités.

La confrontation permanente des acteurs des deux marchés est probablement mieux pratiquée que la diffusion des connaissances. Le TRB Meeting

3 qui se tient tous les ans en janvier à Washington constitue incontestablement un modèle en la matière. Les seuls thèmes relatifs à l'économie des transports et à ses outils réunissent plusieurs milliers de participants issus de tous les organismes concernés : centres de décision, bureaux d'étude, universités, etc. En Europe, mis à part l'expérience du PTRC, modestement suivie hors Royaume Uni, rien de comparable n'est proposé à l'ensemble des acteurs concernés. Les seules rencontres systématiques qui rassemblent toutes les familles d'acteurs sont les Tables Rondes de la CEMT. Leur rôle, dans cette fonction de confrontation, reste très important mais limité à quelques sujets par an et, pour chaque Table Ronde, à une trentaine de participants. Dans la même logique, des colloques ouverts à tous les intéressés jouent également un rôle non négligeable. Mais au total, il manque un équivalent européen du TRB Meeting, dont la régularité permet de programmer de longue date les participations, dont la qualité est assurée et dont l'esprit est propice à la confrontation des deux "mondes".

On doit, en revanche, noter l'important développement de programmes européens de recherche (les Programmes-Cadres"), qui ont, au fil du temps, progressé dans la pertinence des sujets et favorisent de mieux en mieux les collaborations entre bureaux d'étude et équipes universitaires. Les milieux de la décision s'y trouvent, certes, moins impliqués mais l'efficacité académique et l'efficacité sociale y font bon ménage.

Enfin, la mobilité professionnelle entre les sphères académique et décisionnelle est très diversement pratiquée selon les pays. Il est évident que cela constitue un moyen privilégié de transfert d'expérience et, plus généralement, de reconnaissance réciproque entre ces deux sphères. Mais là où cette mobilité est particulièrement faible, comme en France, les raisons sont certainement trop profondes pour qu'un changement puisse être entrevu à court terme.

Figure 2 .

 2 Figure 2. La culture de méfiance

Figure 3 .

 3 Figure 3. La culture de l'échange


MRes Maël Dieudonné
email: mael.dieudonne@univ-lyon2.fr

Does electromagnetic hypersensitivity originate from nocebo responses? Indications from a qualitative study Author

Keywords: Idiopathic Environmental Intolerance, IEI-EMF, Illness Narratives, Attribution Process, Causal Reasoning

Idiopathic Environmental Intolerance attributed to Electromagnetic Fields (IEI-EMF) is a condition in which symptoms are attributed to electromagnetic fields (EMF) exposure. As electrohypersensitive (EHS) people have repeatedly been observed, during provocation trials, to report symptoms following perceived rather than actual exposure, the hypothesis has been put forward that IEI-EMF originates from psychological mechanisms, especially nocebo responses. This paper examines this hypothesis, using data from a qualitative study aimed at understanding how EHS people come to regard themselves as such. Forty self-diagnosed EHS people were interviewed. A typified model of their attribution process was then elaborated, inductively, from their narratives. This model is linear and composed of seven stages: (1) onset of symptoms; (2) failure to find a solution; (3) discovery of EHS; (4) gathering of information about EHS; (5) implicit appearance of conviction; (6) experimentation; (7) conscious acceptance of conviction. Overall, the symptoms appear before the subjects start questioning the effects of EMF on their health, which is not consistent with the hypothesis that IEI-EMF originates from nocebo responses to perceived EMF exposure. However, such responses might occur at the sixth stage of the process, potentially reinforcing the attribution. It remains possible that some cases of IEI-EMF originate from other psychological mechanisms.

Introduction

Idiopathic Environmental Intolerance attributed to Electromagnetic Fields (IEI-EMF) is a condition attributed to electromagnetic fields (EMF) exposure. Its onset seems relatively recent: the first cases were reported in Sweden in the beginning of the 1990s [START_REF] Bergqvist | Possible health implications of subjective symptoms and electromagnetic fields. A report prepared by a European group of experts for the European Commission[END_REF]. In France, where this study was conducted, the earliest testimonies of people claiming to suffer from "electro-hypersensitivity" (EHS) were published in 2006. Since the number of purported sufferers has increased gradually (by July 30, 2015, 1,218 people had registered with the national support group "E.H.S. Entraide"). In France still, EHS started to receive media coverage in 2007 [START_REF] Chateauraynaud | Le partage de l'hypersensible : le surgissement des électrohypersensibles dans l'espace public[END_REF], and is a growing concern for health and industrial authorities.

The combination of several observations suggests a psychogenic origin for this condition. From a clinical point of view, the physical symptoms attributed to EMF exposure, either in daily life or in experimental contexts, are both various and non-specific: the most commonly reported are fatigue, headaches, cognitive difficulties, memory loss, insomnia, cutaneous rashes, and pain in numerous locations [START_REF]Electromagnetic hypersensitivity: The opinion of an observer neurologist[END_REF][START_REF] Hagström | Electromagnetic hypersensitive Finns: Symptoms, perceived sources and treatments, a questionnaire study[END_REF][START_REF] Baliatsas | Actual and perceived exposure to electromagnetic fields and non-specific physical symptoms: An epidemiological study based on self-reported data and electronic medical records[END_REF]. No physiopathological mechanism has been proven to be involved, notably because a recurring association between the onset of symptoms (or of objectively measured physiological changes) among EHS subjects and their exposure to EMF has not been observed in experimental settings [START_REF] Röösli | Radiofrequency electromagnetic field exposure and non-specific symptoms of ill health: a systematic review[END_REF][START_REF] Rubin | Idiopathic environmental intolerance attributed to electromagnetic fields (formerly "electromagnetic hypersensitivity"): An updated systematic review of provocation studies[END_REF][START_REF] Rubin | Do people with idiopathic environmental intolerance attributed to electromagnetic fields display physiological effects when exposed to electromagnetic fields? A systematic review of provocation studies[END_REF]. Besides, the devices typically blamed by these subjects (e.g., mobile phones and base stations, and WiFi routers) are not known for triggering adverse biological effects in their standard conditions of use (that is, at levels of exposure too low for thermal effects to occur) [SCENIHR, 2015]. People labeling themselves EHS also seem to experience higher levels of stress, anxiety, depression and somatization than the average person [START_REF] Johansson | Symptoms, personality traits, and stress in people with mobile phone-related symptoms and electromagnetic hypersensitivity[END_REF].

All these observations indicate that IEI-EMF might be classified among functional somatic syndromes (FSS) [START_REF] Barsky | Functional somatic syndromes[END_REF], or symptom-based conditions [START_REF] Hyams | Developing case definitions for symptom-based conditions: the problem of specificity[END_REF]. They also explain why it remains an essentially self-reported condition, lacking an objective and unambiguous case-definition [START_REF] Baliatsas | Idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF): A systematic review of identifying criteria[END_REF]. In this paper, the term EHS is used to refer to this subjective aspect of IEI-EMF (conversely, the term IEI-EMF is employedas it was defined during the World Health Organization 2004 Prague workshopto designate the illness that may account for the symptoms experienced by subjectively EHS people [START_REF] Hansson Mild | Electromagnetic Hypersensitivity: Proceedings, International Workshop on EMF Hypersensitivity[END_REF]).

Additional results bring forward the more specific hypothesis of an involvement of nocebo responses in this condition: the observation of a consistent correlation between the number and intensity of the symptoms reported by EHS subjects in provocation trials, and perceived exposure [START_REF] Oftedal | Mobile phone headache: a double blind, sham-controlled provocation study[END_REF][START_REF] Eltiti | Aggregated data from two double-blind base station provocation studies comparing individuals with idiopathic environmental intolerance with attribution to electromagnetic fields and controls[END_REF]. Nocebo response is a term originally crafted to designate the occurrence, after the administering of a medication, of symptoms or adverse physiological changes that cannot be explained by its pharmacological properties, and are therefore attributed to the patients' expectations or unconscious reactions. Its existence has been demonstrated beyond doubt in the context of clinical trials [START_REF] Barsky | Nonspecific medication side effects and the nocebo phenomenon[END_REF]. Moreover, several well-established physiological mechanisms can explain its functioning: the stress response [START_REF] Chrousos | The concepts of stress and stress system disorders. Overview of physical and behavioral homeostasis[END_REF], panic attacks [START_REF] Staudenmayer | Environmental Illness: Myth and Reality[END_REF], or conditioning and learning [START_REF] Benedetti | Conscious expectation and unconscious conditioning in analgesic, motor, and hormonal placebo/nocebo responses[END_REF] though there is no apparent consensus on the exact mechanism involved [START_REF] Jakovljevic | The placebo-nocebo response: controversies and challenges from clinical and research perspective[END_REF]. The nocebo response thus appears as a convincing explanation of EHS subjects' reactions in experimental settings, and to a certain extent, of the symptoms they experience in daily life. Indeed, they tend to express more concern over pollution and toxic agents in their environment than healthy controls [START_REF] Rubin | Psychological factors associated with self-reported sensitivity to mobile phones[END_REF], and some of the personality traits they display (notably anxiety and somatization) are regarded as enhancing nocebo reactivity [START_REF] Barsky | Nonspecific medication side effects and the nocebo phenomenon[END_REF].

These elements lead to the understanding of IEI-EMF as the result of a vicious circle, in which negative expectations about the health effects of EMF exposure increase the awareness of EMF sources in the environment, as well as the monitoring of bodily sensations, bringing nocebo-prone people to discover or amplify symptoms when they feel they are exposed. This confirms their expectations, and fuels a cycle of nocebo responses that operates until and after they label themselves EHS [START_REF] Szemerszky | Polluted places or polluted minds? An experimental sham-exposure study on background psychological factors of symptom formation in "Idiophatic Environmental Intolerance attributed to electromagnetic fields[END_REF][START_REF] Witthöft | Are media warnings about the adverse health effects of modern life self-fulfilling? An experimental study on idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF)[END_REF]. But how does this cycle start? Are media warnings about EMF health effects sufficient, as these authors assert, when they meet with personality traits enhancing nocebo responsiveness? Do they deserve to be described as "polluting minds" [START_REF] Szemerszky | Polluted places or polluted minds? An experimental sham-exposure study on background psychological factors of symptom formation in "Idiophatic Environmental Intolerance attributed to electromagnetic fields[END_REF] and "self-fulfilling" [START_REF] Witthöft | Are media warnings about the adverse health effects of modern life self-fulfilling? An experimental study on idiopathic environmental intolerance attributed to electromagnetic fields (IEI-EMF)[END_REF]? If not, are other psychological mechanisms involved in the formation of the symptoms experienced by EHS people? Despite the growing body of research devoted to IEI-EMF, virtually no observational data is available to test these hypothesis, and little is known about the series of experiences and events that lead EHS people to perceive themselves as such. This paper presents the results of a qualitative study, which was carried out to understand this phenomenon. It formulates a typified model of the underlying attribution process, and discusses whether it fits with the hypothesis of an involvement of nocebo responses, or other psychological mechanisms, in the genesis of IEI-EMF.

Materials and methods

No method has been proposed nor validated to examine the attribution process of EHS people.

This study was therefore conducted with an inductive approach, and must be considered explanatory.

Participants

For a first approach, the most straightforward method appeared to focus on people genuinely convinced of their condition. To ensure this was the case, two inclusion criteria were used: the claim to suffer from EHS, evidently, and the adjustment of one's lifestyle accordingly (e.g., getting rid of one's electronic devices, shielding one's home from EMF, avoiding places deemed exposed, etc.). They proved largely redundant, leading only to the exclusion of a few people from the study: people who considered themselves lightly sensitive to specific devices, but had not modified their lifestyle, and denied they were EHS. They were close relations of EHS people, or activists campaigning against "electromagnetic pollution," who appeared cautious rather than sick. They likely correspond to the mild form of IEI-EMF observed by some authors [START_REF] Rubin | Psychological factors associated with self-reported sensitivity to mobile phones[END_REF][START_REF] Johansson | Symptoms, personality traits, and stress in people with mobile phone-related symptoms and electromagnetic hypersensitivity[END_REF].

The participants (11 men and 29 women, mean age 51±11 years) were recruited by means of an announcement sent on several mailing lists of EMF-sensitive people, direct requests during EHS support groups meetings, and by word of mouth through personal networks. The sample was diversified as much as possible in terms of social and illness features. Its size (n = 40) was determined using the saturation principle [START_REF] Mason | Sample size and saturation in PhD studies using qualitative interviews[END_REF]. The demographic characteristics of the subjects are presented in Table 1. The symptoms they attribute to EMF exposure are detailed in Table 2, and the number of symptoms they reported in Table 3. The perceived sources of exposure are listed in Table 4.

Interviews

An essential aspect of coping with a chronic illness is the elaboration of an "illness narrative": a structured story that arranges the memories and experiences of the ill person in a meaningful way, giving a sense to his or her suffering, and allowing to convey it to others [START_REF] Kleinman | The Illness Narratives: Suffering, Healing, And The Human Condition[END_REF]. The challenge is therefore to reconstitute the original course of events (what can be called the "factual biography") from these "narrative reconstructions" [START_REF] Williams | The genesis of chronic illness: narrative re-construction[END_REF].

For that purpose, a two-steps method of interviewing was used. The subjects were initially presented with a broad question ("How did things happen for you?"), to which they could answer freely, for as long as they wished. Then specific questions were asked following a detailed interview guide, about (1) their symptoms, (2) their ways of coping with them, (3) how they came to attribute them to EMF exposure, (4) their perceived effects on their social relationships, and (5) their main social characteristics. By enabling comparison between the narrative first told by the subjects and the specific answers they give afterward, this method facilitates the detection of retrospective shifts of memories (the most significant that was observed being a tendency to overlook the active part they took in the construction of EHS as a convincing explanation of their predicament).

The common tricks of the qualitative investigator [START_REF] Becker | Tricks of the Trade: How to Think about Your Research While You're Doing It[END_REF] were employed to obtain accurate information (e.g., rephrasing the questions, repeating them at different times in the interviews, saving the sensitive ones for the end, asking "how?" rather than "why?", etc.). At the same time, great care was taken not to suggest answers. The questions were formulated in an open and neutral way, as in the following examples: "Can you describe precisely what you feel when you're exposed? What convinced you that EMF exposure was responsible for your symptoms? Do you ever doubt it? How do you distinguish between the symptoms triggered by EMF exposure, and those resulting from other causes?" When the subjects appeared hesitant, they were asked about the precision of their memories and their degree of certainty.

Lastly, precautions were taken against the desirability bias. To create a climate of trust, and avoid the participants being stressed by the confrontation with an unknown environment, the interviews were conducted in venues of their choice (mostly their homes). The investigator was careful about turning off all electronic devices prior to approaching each of them. He wore no perfume nor freshly washed clothes in case they were sensitive to chemicals, and displayed an understanding and benevolent attitude. Overall, the subjects responded very positively to these efforts. They regularly thanked him for offering them an opportunity to speak unashamedly of their condition, and willingly assisted in the reconstitution of their factual biographies.

Detailed information was thus collected with a relatively low risk of inaccuracy. The interviews were conducted in rural and urban areas of France between February 2012 and September 2013.

There average duration was 143 min. They were consistently recorded, and transcribed for analysis.

Data analysis

It quickly appeared that diagnosing themselves EHS had not been obvious for the subjects, but was rather the outcome of long and distressing trajectories, involving many dimensions of their lived experience (somatic perceptions, emotions, thoughts, behaviors, interactions with others, etc.).

Gradually, a few typical circumstances all of them had gone through, seemingly in the same order, became apparent. The analysis was then directed toward understanding how these were connected, that is, how the subjects had passed from one set of circumstances to the next, and so forth, until they became truly convinced they were EHS. It was conducted under three assumptions: (1) that their factual biographies could be analyzed as following a logical sequence (the attribution process);

(2) that the progression of this sequence could be accounted for by bringing together all significant dimensions of the subjects' experience at each of its stages; and (3) that some elements of their experience might not appear explicitly in their discourses, but might be inferred from their behaviors and thoughts.

A single synthetic model of the attribution process was thus obtained. It was then cross-checked for consistency with each of the subjects' factual biographies, even though it does not aim at describing them: it focuses on their most determinant features, so as to explain their relations and the forms they take. Hence it is a pure type, in the Weberian sense. This method is more ambitious than the one consisting in listing the main themes of the subjects' discourses, as applied by [START_REF] Nettleton | Understanding the narratives of people who live with medically unexplained illness[END_REF] to patients with medically unexplained symptoms (MUS), or [START_REF] Dumit | Illnesses you have to fight to get: facts as forces in uncertain, emergent illnesses[END_REF] to sufferers of chronic fatigue syndrome (CFS) and multiple chemical sensitivity (MCS): it presents more risk, but can yield results having a better explaining power.

Results

The typified attribution process underlying the subjects' factual biographies is linear and composed of seven main stages. Each is illustrated with significant excerpts from the interviews.

Stage 1onset of symptoms

Disturbing or incapacitating symptoms appear and develop until they become unmanageable. This might happen either progressively (over the course of several years) or suddenly (within a few weeks), but always results in a "biographical disruption" [START_REF] Bury | Chronic illness as biographical disruption[END_REF] (i.e., an inability to fulfill one's professional and/or domestic duties), which reveals the abnormality of the symptoms.

Stage 2failure to get a (medical) solution

The subjects seek treatment for their ailment from general practitioners, medical specialists or alternative therapistsmost of the time from them all, because none of the treatments offered prove effective in the long term. So they fail to restore the normality of their situation. Furthermore, they also fail to get a conventional diagnosis, which means they are denied the possibility of legitimately endorsing the sick role, and make the abnormality of their situation socially acceptable (some subjects managed to get diagnosed with a "contested illness" [START_REF] Conrad | The social construction of illness. Key insights and policy implications[END_REF] like fibromyalgia (6 subjects) or late Lyme disease (5 subjects), which proved of little avail as in France, these conditions are not generally recognized by medical authorities and social services). This leaves them feeling profoundly distressed and stigmatized, as most patients with MUS [START_REF] Nettleton | Understanding the narratives of people who live with medically unexplained illness[END_REF], or CFS and MCS sufferers [START_REF] Dumit | Illnesses you have to fight to get: facts as forces in uncertain, emergent illnesses[END_REF]. The length of this stage varies greatly also.

"I found myself on the ground. Because of chronic pain. Something infernal. The doctors groped around for three years, and for three years they believed I was going to die. They looked for everything: a cancer, AIDS, AIDS-related illnesses, lots of viruses, tropical diseases, and so on.

Stage 3discovery of EHS

The previous stage comes to an end when the subjects happen to learn about EHS, in which they catch a glimpse of an explanation for their ailment. This encounter can occur through different media: a radio show, a newspaper article (usually from the local or militant press), a talk with friends or relativesbut very rarely the Internet. It implies the same content: the testimony of an alleged EHS sufferer, in which they recognize themselves ("what he was telling, that was me, that was what I was living"). This moment is experienced as a genuine revelation. It goes along with a vertiginous questioning ("what if EHS is what I'm suffering from?"), that expresses a psychological tension between the hope of a relief (having finally identified the disease that is affecting them) and the fear of a disappointment (having identified the wrong disease).

"For me it was at work. I was on the computer, and a colleague told mebecause they could see I was breaking down. They saw me, I was about to freak out. And so they told me: 'yeah, you know, I've seen a TV show, heard of, there are people who are hypersensitive to radiowaves. Could you have it?' Then we looked on the Internet, and voilà, we saw... Well at that time, in 2006, there wasn't much. There were a couple of testimonies, and it's true that when looking at the symptoms, when comparing the symptoms, they were exactly those I had.

Insomnia, headaches, difficulty in concentrating, dizziness... Exactly the aches that... So, that's how I reached that conclusion." [Woman,aged 45] Stage 4gathering of information about EHS The third stage is very brief, since the subjects immediately begin to gather information on EHS, in a rather compulsive manner. They consult the Internet first, then solicit support groups, small but active associations campaigning against wireless communications, and companies selling EMF protection devices. This information typically concerns the other sufferers' symptoms and the devices to which they attribute them. Its analysis causes a shift of the emotional conflict, i.e., a displacement of the focus of relief ("I suffer from a real disease, I'm not crazy, it's not all in my head") and still more, of the focus of fear (in anticipation of the multiple constraints associated with this condition, revealed by catastrophic testimonies: "how am I going to live?"). This stage is short but extremely intense, the subjects tending to devote all their available time to their investigation ("I needed to know"). It also proves emotionally taxing.

Stage 5implicit appearance of conviction

The conviction that they are EHS appears in the subjects' minds, but seemingly escapes their awareness: they start reasoning as if they were sensitive to EMF, while consciously doubting they are (as observed in the next stage). Arguably, this happens after relief has (even temporarily) prevailed over fear: a quarter of the subjects (10) have emphasized how important it had been to succeed in alleviating their symptoms the first time they knowingly attempted to reduce their exposure to EMF. For 9 subjects, this implicit conviction has taken the paradoxical form of a deliberate and violent rejection of the diagnostic of EHS ("I don't want this illness, it's too bad!").

Stage 6experimentation

The subjects initiate an active verification procedure, conducting small experiments to confirm the existence of a relationship between their health state and their electromagnetic environment. Their realization requires them to learn several things: 1. Which devices emit EMF. Initially the subjects only know (at best) about mobile phones and base stations, and WiFi routers; but soon enough they discover that cordless phones, fluorescent lamps, computers, TV sets, smoke detectors, etc., also radiate (considering indistinctly radio frequency and extremely low frequency sources).

2. How to identify these devices in their environment: either by direct visual observation (e.g., spotting antennas on the buildings close to their homes); indirectly by using various EMF sensors (e.g., radio frequency power meters, low-level magnetic fields strength meters, or indicators for electric fields in the ELF rangepreferably those which provide visual or acoustic indications); or even vicariously by looking for informants (e.g., technicians in their workplace about WiFi networks, or neighbors about cordless phones in their homes).

3. How to protect themselves from EMF (e.g., by turning some devices off, sleeping under a shielded canopy, wearing shielded garments, etc.).

The subjects thus become able to link their symptoms to EMF exposure, in a distinctly adversarial manner. For instance, they do not admit any threshold in their sensitivity: every exposure they manage to identify, whatever its source, power or duration, is regarded as a plausible cause of their symptoms. Similarly, when they find themselves unable to identify a source of exposure, they tend to discard the possibility that such a source is absent. This remarkable imperviousness to disproof justifies to regard them as implicitly convinced that they are sensitive to EMF.

At the end of this sixth stage, the diagnosis of EHS appears as a persuasive explanation for their ailment. It also proves somewhat effective in coping with it, not least because it provides them with a sense of control.

Stage 7conscious acceptance of conviction

The emotional conflict having now been resolved, the conviction that they are EHS becomes bearable for the subjects, and reaches the conscious level. The ability to demonstrate its independence from their will, stemming from the experiments they have conducted, likely plays a decisive role in this process (as indicated by their tendency, in their illness narratives, to overlook the desire they had to find an explanation for their ailment: "I was really skeptical but was forced to believe"). The subjects now regarding themselves as EHS sufferers, start knowingly adapting their lifestyle, rewriting their personal stories to make them coherent with their new belief system (i.e., constructing their illness narratives), and sometimes campaigning for the official recognition of their condition.

"First you need, not to convince yourself, but to accept that that's it. […] That's why I was doing blind tests and all, because you do everything you can to say to yourself: 'well,no.'" [Man,aged 51] "What EHS sufferers are often reproached with is their obsession about it. But once you have understoodyou have rebuilt the puzzle and understood that all your miscellaneous symptoms were due to it, once you recognize the headaches, which I tell you are no sinusitis, are no viruses, are really very specificyou know it's that." [Woman,aged 33] This goes along with a transformation of their attitude towards somatic perceptions: they cease putting their reality in doubt when faced with dissonant elements (e.g., if they fail to identify a source of exposure after the onset of symptoms).

"The sensor detects one second after me. And there are places where it's not sensitive enough, and I feel too many things, and it shows nothing. Moreover, when I turn it on it hurts me, I feel it. So it must concentrate, I think, the waves around it. […] I have it just in case, to check for people, but as for me, I prefer to see things by feeling myself.

-Do you trust yourself more than the sensor? -Exactly. Furthermore because afterwards, you need to know how to interpret the sensor data.

I prefer to interpret my feeling. And even if it's a bad place and I feel good, why not, I mean, it's the body which answers, which speaks." [Woman,aged 52] Consequently, the subjects did not seem to differ by their degree of certainty (though this is difficult to assess comparatively). They were not more or less convinced they were EHS, but rather convinced they were more or less EHS, and in different ways. In their view, as the investigator has regularly been told, "there are as many sensitivities as hypersensitive people."

Discussion

The most significant feature of the subjects' typified attribution process is that the symptoms onset before the environment is suspected, and EMF exposure is interpreted as noxious and held responsible for them. How long before is difficult to quantify because the subjects did not always remember exactly when their symptoms appeared (which is unavoidable when it dates back several years). But there is no doubt they were already feeling sick (stage 1)because they had sought, and failed to obtain, medical assistance (stage 2)when they started questioning the effects of EMF in their environment on their health (stage 4). Furthermore, only 5 subjects knew precisely what EMF were at the time their symptoms began (they were working as teachers or engineers, and had studied physics). Twelve other subjects had been cautioned in the past against specific EMF-emitting devices: mobile phones and WiFi routers mostly, either by a relative, an alternative therapist they were consulting, or a news report. However, they did not remember having been warned against EMF health effects in general, and did not start feeling concerned until they fell ill and discovered the existence of EHS (stage 3). The 23 remaining subjects had never heard of EMF before reaching the same stage in the attribution process. Arguably, had they been initially convinced of the harmfulness of EMF exposure, they would not have felt such an urge to gather information about it (stage 4), nor to establish so attentively its correlation with their symptoms, so as to prove to themselves they are indeed EHS (stage 6).

Therefore, it seems highly implausible that their ailment originates from adverse expectations related to EMF. The vicious circle of IEI-EMF, assuming the corresponding model is correct, is unlikely to be triggered by media (or personal) warnings, even in conjunction with personality traits enhancing nocebo responsiveness: rather, it adds to preexisting conditions, resulting precisely from their sufferers' struggle to understand them. This does not imply, however, that nocebo responses are not involved in the genesis of IEI-EMF.

Nocebo and placebo responses in the attribution process

First, they are likely to occur at one point of the attribution process: when the subjects start scrutinizing their electromagnetic environment, especially if they resort to EMF sensors (stage 6). This behavior leads them to observe the ubiquity of EMF, which arouses negative expectations and anxiety. Remarkably, a few subjects (3) seemed aware of this reaction, relating how they committed themselves to abandoning their scrutinizing behavior due precisely to the worry they were causing themselves. Similarly, placebo responses might intervene slightly earlier in the attribution process, the first time the subjects try to relieve their symptoms through reducing EMF exposure. Doing so with high hopes and expectations, they meet with instantaneous success ("I turned my WiFi router off and immediately, all my symptoms disappeared")while the following attempts, whose outcome is taken for granted, generally prove less fortunate. The attribution process thus has strong emotional implications (stage 5 and 7), which might promote nocebo and placebo responses and have somatic consequences (inducing new symptoms, aggravating the existing ones, or alleviating them). These might in turn contribute to the subjects' progression through the attribution process, promoting the perception of EHS as a convincing explanation of their ailmentalthough it does not seem likely for all of them.

The case for unconscious conditioning and "technological stress"

A possibility remains for nocebo responses to account for the genesis of the ailment attributed to EMF: that they do not involve conscious expectations related to EMF, but rather unconscious processes as part of a conditioning mechanism. Such a hypothesis was originally put forward to account for the symptoms attributed to visual display units (VDU) in occupational settings [START_REF] Arnetz | Technological stress: psychophysiological symptoms in modern offices[END_REF]. It builds upon the observation that the use of new technological devices is frequently a source of stress, especially for motivated workers who regard their job as stimulating, but feel they lack the appropriate skills. This "technostress" might cause them to regularly experience symptoms, and get conditioned to their work environment. However, they would focus on these new devices, or other elements in their workplaces, when searching for an explanation of their ailmentand find it in the EMF they generate. They would then start reacting adversely to other devices identified as emitting EMF, even outside of their workplace, because of conscious expectations triggering nocebo responses. They would eventually develop a severe form of IEI-EMF, and label themselves EHS. This hypothesis is supported by the observation that people attributing symptoms to VDU tend to display higher levels of technostress than their colleagues, and that people reporting a sensitivity to mobile phones are also more likely to use their own for work [START_REF] Rubin | Psychological factors associated with self-reported sensitivity to mobile phones[END_REF]. In this study, one participant recounted that his symptoms began at work, and that he managed to connect them to EMF exposure several months later, when he started working with a wireless modem. Another participant declared his symptoms originated in an occupational use of computers. None of them mentioned difficulties in using these devices (they were both technology enthusiasts), or workrelated stress. Five other subjects reported they were experiencing such stress when their symptoms first appeared, but linked them with EMF exposure through devices in their homes.

Thus, the hypothesis of unconscious conditioning somewhat fits with the factual biographies of a few subjects, indicating that some cases of IEI-EMF might originate from technological stress.

However, if it explains the origin of the symptoms, it does not account for their attribution to EMF, and cannot be substituted to the process presented above.

Implications for the understanding of IEI-EMF

Overall, these observations suggest that EHS people would be better conceived as patients suffering from MUS, which they come to attribute to EMF exposure. This attribution allows them, firstly to make sense of those symptoms, then to act upon them: it is a means of empowering themselves against their ailment. This perspective has significant implications for the understanding of IEI-EMF.

First, the responsibility of media warnings about EMF health effects in the development of this condition should not be overestimated. They certainly affect, and likely shape, the perception of EMF risk [START_REF] Burgess | Cellular Phones, Public Fears, and a Culture of Precaution[END_REF]. But to its sufferers, IEI-EMF does not initially appear as a risk, but as an explanation for their ailment. Furthermore, media warnings hardly contribute to the credibility of this explanation compared to the sharing of testimonies with other EHS people, the discovery of information on how to cope with EMF exposure, and personal experiments. Thus, their effect is essentially to make EHS widely available as a potential diagnosis for people suffering from MUS.

Second, people with IEI-EMF should be distinguished from "modern health worriers" (MHW) [START_REF] Petrie | Thoroughly modern worries: the relationship of worries about modernity to reported symptoms, health and medical care utilization[END_REF], whose concerns make them more likely to react adversely during provocation trials, but who have no need nor reason to diagnose themselves EHS, since they do not necessarily suffer from persistent, incapacitating, and "medically unexplainable" symptoms. Alternatively, the presence of such symptoms might characterize a severe form of IEI-EMF, while MHW could be regarded as presenting its mild form (there is little empirical indication that these two forms constitute a homogeneous clinical entity, and should be analyzed identically).

A third implication is that people with IEI-EMF should also be distinguished from IEI sufferers.

These attribute symptoms to chemicals in their environment, which they seem to identify through their sense of smell. Many have been observed, in experimental settings, responding to olfactory stimuli [START_REF] Das-Munshi | Multiple chemical sensitivities: A systematic review of provocation studies[END_REF]. This makes it rather straightforward for them to connect their symptoms to their environment: perceiving chemicals directly, they do not need to reveal their presence retrospectively, for instance by using sensors, as EHS people do. Consequently, the involvement of unconscious conditioning mechanisms in the formation of their symptoms appears more likely [START_REF] Meulders | Resistance to extinction in an odor-20% CO2 inhalation paradigm: further evidence for a symptom learning account of multiple chemical sensitivity[END_REF] especially since many cases of IEI have been reported to occur after a massive exposure to some chemical substance [START_REF] Staudenmayer | Environmental Illness: Myth and Reality[END_REF].

Fourthly, regarding IEI-EMF as consisting in the attribution of MUS to EMF exposure incites to apprehend it less as a homogeneous clinical entity, than as a label covering miscellaneous ailments.

Various causes should then be considered for the symptoms originally experienced by EHS people: technostress and unconscious conditioning, as seen above, undiagnosed chronic illnesses or psychiatric conditions, dysregulation of the autonomic nervous system [START_REF] Sandström | Holter ECG monitoring in patients with perceived electrical hypersensitivity[END_REF] potentially amplifying the responsiveness to sensory stimuli [START_REF] Nordin | Odor and noise intolerance in persons with selfreported electromagnetic hypersensitivity[END_REF], actual sensitivity to EMF, etc.

Limitations

The first limitation of this study derives from its qualitative nature. The data is only as accurate as the subjects' perceptions and memories, and the eventuality cannot be excluded that some bias have not been adequately controlled for during the interviews. Besides, the non-implementation of a conventional method of sampling precludes estimating the representativeness of the sample. Care should thus be taken before generalizing the results.

More specifically, a second set of restrictions stems from the design of this study. The inclusion criteria as well as the recruitment strategy might have led to the enrollment of participants with a rather severe form of IEI-EMF [START_REF] Van Dongen | Symptom attribution and risk perception in individuals with idiopathic environmental intolerance to electromagnetic fields and in the general population[END_REF], and there is no indication that the genesis of its mild form can be accounted for by the proposed model of the attribution process. The functioning of this model may also be affected by the psychological characteristics of the subjects, which were not objectively assessed. Moreover, its efficiency is difficult to evaluate, for the investigator was unable to discover people having either seriously thought they might be EHS and concluded they were not, or having regarded themselves as EHS and subsequently ceased to. This is not surprising as such people would predictably leave the EHS network, thus becoming difficult to identify. Still, their cases would be interesting to document. Finally, as this paper is focused on the genesis of IEI-EMF, it only deals with the factual biographies of EHS people until they become convinced they are EHS; it does not address what happens after, and does not reflect the diversity of personal situations in which EHS people can actually be found.

Conclusion

The results of this study are not consistent with the hypothesis that severe IEI-EMF is a condition originating from nocebo responses to perceived EMF exposure, even though it is likely to be aggravated, after its onset, by a vicious circle of such responses. These results do not indicate either, that other psychological mechanisms are systematically involved in the formation of the symptoms initially experienced by EHS people (i.e., before they come to regard themselves as such). Rather, they suggest to consider EHS as a label applied by some MUS sufferers to their ailment, in their struggle to make it emotionally and practically manageable. This arguably justifies the clinical and experimental elusiveness of IEI-EMF, and the ongoing inability to define it objectively, which are likely accentuated by the generic nature of the attribution process. The fact that it functions with virtually every type of symptoms might explain why the efforts to reduce the subjective aspects of IEI-EMF have hardly made it a less perplexing condition. Fluorescent lamps 9

Computers (system units) 8

Screens (computer displays and TV sets) 6

Cars 4

Other sources 7

"

  Do you want me to talk about the doubts one can have? And especially the fears, when you say: No, I don't want to be electrosensitive! It's the others who emit too much. And there are places where you feel good, so you are not electrosensitive. Then you see there are more and more places where you feel ill." [Man, aged 54]

"

  Actually, I was walking in the street, I was feeling it, I was raising my head, there was an antenna.[…] Or I was in a room with someone, I felt it, and two seconds later his mobile phone rang. So gradually I discovered, I was telling myself: 'damn, I'm a sensor.'" [Woman, aged 41] "Now I notice that my body is more receptive than my EMF sensor, so even if the sensor shows nothing, the body may perceive. When this happens, I need to move a little with the sensor, and I quickly find the pollution source. So far, I've never had a WiFi sensation, without finding a WiFi nearby. That is to say I've never dreamed it. If my sensor detects nothing, I go out and five meters away I find one."[Woman, aged 55] "I'm taking a music lesson and I warn people that I faint with... with cell phones. And then I really get the proof it wasn't psychosomatic, because I faint nonetheless, even if everybody was warned. […] So I learn, after fainting, that there was indeed someone making a phone call in the next room: 'yes, so as not to disturb you.' So if I could feel the waves through the walls, that was the proof[that I was EHS]."[Woman, aged 57]

"

  As soon as I realized what it was, there was a psychological effect. Things got a little worse, because I was identifying [the exposures]." [Man, aged 39]"The more I observed [my environment] to avoid exposing myself, to avoid fainting, the more sensitive I was."[Woman, aged 57]

  By the time it ended in 2009, I could do absolutely nothing but work. I had been compelled to employ a cleaning lady because I couldn't event do the housework." [Woman, aged 59] "Then gradually, at the office […] I could not figure out what people were asking me. I felt confused, as if my eyes were going back into the orbits, as if I had a constant strain in my eyes.

	And twinges of pain, the skull squeezed -in short, a whole set was beginning to put itself in
	place, and I was starting to feel very ill, I mean truly ill, as if I was being affected by something,
	and I could not understand what was happening." [Woman, aged 58]

"To be honest, I used to be hyperactive. And then suddenly, boom! nothing. Well it wasn't that sudden, it took two years. I grew weaker and weaker, I could do fewer and fewer things, I couldn't knit I couldn't read.

[…]

  For five year I didn't get a diagnosis, no one could tell me what I was suffering from. […] To begin with, you go and see your physician, because when you fall ill the only person you're thinking of consulting is your physician. You have no choice, you've been raised that way, you'll never think of turning to alternative medicines. Then I don't know, after three or four years, you say: 'okay, medicine, allopathy is powerless.' You begin to turn to alternative medicines. You go to a homeopath, you go to an iridologist, you go to a magnetotherapist, you go and see this you go and see that. Well as it turned out, it's the magnetotherapist who did me the best." [Man, aged 46]

"

  Like everyone, I started looking on the Internet. Which is... very good and horrible at the same time. As soon as you suspect a disease or something, that's it. Without delving into the details, you imagine everything you see, everything you read, and so on. And it's true that afterwards, fear makes you feel unable to cope with that thing."[Woman, aged 37]

"

  Now I don't have my pains anymore, so I'm reassured, because I know that... it is possible to recover, there are remedies."[Man, aged 50] "What convinced you, was to see that the advice you were given were effective? -They were very, very effective.-Did you notice the difference immediately? -Well, actually, I never tried again to sleep with the fuses on.[…] Even so it made me feel really strange, I was telling myself: 'what's this delirium, turning off one's bedroom's fuse to sleep? What have I fallen into?' And well, I saw it was working, that's it."[Man, aged 39]

Table 1 -

 1 Demographic characteristics of interviewed subjects Age

	18-24

Table 2 :

 2 symptoms attributed to EMF exposure, by the number of subjects who reported them

	Sleep problems

Table 3 :

 3 number of reported symptoms, by the number of subjects Low (4 symptoms or less) 14

	Medium (5 to 7 symptoms)

Table 4 :

 4 perceived sources of exposure, by the number of subjects who mentioned them

	WiFi routers

Acknowledgements

I am grateful to Jean-Hugues Déchaux for supervising the PhD thesis from which this paper eventuated. A shorter version of it was presented at a conference of the French Society for Radioprotection, in October 2014: I thank the participants for their comments.

I also thank all the subjects who willingly took part in this research.

Grant sponsor

This study was supported by a doctoral grant from the French Ministry of Higher Education and Research (Paris), and was designed and carried out entirely independently.


Sonia Bouzidi

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