Isabelle Chort
email: isabelle.chort@dauphine.fr.

Philippe De Vreyer

Thomas Zuber

Gendered internal migration patterns in Senegal *

Keywords: Internal migration, gender inequalities, rural-urban migration, Senegal JEL classification : R23, J16, O15, O18

Using individual panel data from Senegal collected in 2006-07 and 2010-12, this study explores internal migration patterns of men and women. The data used contain the GPS coordinates of individuals' location, allowing us to calculate precise migration distances and map individual mobilities.Women are found to be more likely to migrate than men. However, they move less far and are more likely to migrate to rural areas, especially when originating from rural areas. Education is found to increase the likelihood of migration to urban destinations, especially for women. An analysis of the motives for migrating confirms the existence of gendered migration patterns, as female mobility is mostly linked to marriage while labor mobility is frequently observed for men.

Introduction

Studies on migration have favored the analysis of international movements and their dynamics. However, largely due to physical, financial and psychological costs, the vast majority of population movements take place within national boundaries (UNDP, 2009).

While internal migration is generally under-documented, this is even more striking in the context of developing countries, especially in Sub-Saharan Africa. Moreover gender differences in access to migration have been little explored. The few studies that have focused on this issue have stressed the limited geographic mobility of women, explained by gender roles or family constraints [START_REF] Kanaiaupuni | Reframing the migration question: An analysis of men, women, and gender in Mexico[END_REF][START_REF] Assaad | Constrained geographical mobility and gendered labor market outcomes under structural adjustment: Evidence from Egypt[END_REF][START_REF] Massey | International migration and gender in Latin America: A comparative analysis[END_REF][START_REF] Chort | Mexican Migrants to the US: What Do Unrealized Migration Intentions Tell Us About Gender Inequalities?[END_REF]. Yet, internal migration plays an important role in social mobility by providing access to employment opportunities [START_REF] Assaad | Constrained geographical mobility and gendered labor market outcomes under structural adjustment: Evidence from Egypt[END_REF][START_REF] Brauw | The role of rural-urban migration in the structural transformation of Sub-Saharan Africa[END_REF]. Uncovering the different determinants of women's and men's migration patterns can contribute to reduce the gap between male and female migration rate by informing policies aimed at promoting labor-market oriented female mobility.

The aim of this paper is to study the gender-specific determinants of internal migration and distance travelled in Senegal. We use individual panel data from a nationally representative survey collected in 2006-2007and 2010-2012 (Poverty and Family Structure survey). Our data are unique first in that all individuals in the household are tracked, within the country boundaries, whatever their relationship to the household head. They thus provide us with a direct information on internal migration, which is rare in developing countries, and even more in sub-Saharan Africa [START_REF] Brauw | The role of rural-urban migration in the structural transformation of Sub-Saharan Africa[END_REF].

Second, our data contain the GPS coordinates of individuals' location in both waves.

We are thus able to calculate distances precisely and map individual mobilities, avoiding limitations and constraints of migration definitions based on administrative units. In addition, the PSF survey includes several modules containing valuable demographic and economic information at the individual, household, and community levels, which allows us to analyze a large set of economic and non-economic determinants of internal mobility.

We use in addition data from the 2002 Senegalese census to investigate the role of migration "push-factors" at the sub-regional level (département). The econometric analysis of the determinants of migration decision, distance travelled and rural or urban location is complemented with a descriptive study of migration motives and a mapping of individual moves using cartographic tools.

The econometric analysis first reveals that women are more likely to migrate than men.

A careful analysis of attrition between the two survey waves nuances this observation as the attrition rate is significantly higher for men, which suggests that women who migrate are less likely than men to live alone and be lost with their entire household, or to lose contact with their origin household. Consistent with this interpretation, we find that the distance travelled is significantly lower for women than for men. We find that women are more likely than men to experience rural-to-rural migration and that for women this kind of migration is associated with marriage. Importantly, education is found to increase both men and women's probability of migrating to urban areas. This article makes several contributions. First, it increases our knowledge of Senegalese internal migration by providing a comprehensive picture of internal migration and its determinants in contemporary Senegal based on individual panel data. By combining survey and census data this article simultaneously considers individual, household, community and regional determinants of migration and distance travelled. This study thus complements and extends the analysis by [START_REF] Herrera | Determinants of Internal Migration among Senegalese Youth[END_REF] Second, this article focuses on gender differences in internal migration patterns which have been largely overlooked. An analysis of migration motives declared in our data (see Figure 3) reveals drastic differences between men and women. A large share of female migration is driven by family motives, the most important of them being marriage. By contrast, the proportion of women migrating for labor-related reasons is low, while labor is the primary migration motive for men. Such observations suggest little evolution in the last 30 years, as the conclusion by [START_REF] Chant | Gender & migration in developing countries[END_REF] based on numerous case studies in the developing world are unchallenged: in contemporary Senegal, women are less likely than men to migrate independently for employment. This specific feature of female internal migration being largely associated with marriage is common to many sub-Saharan African countries [START_REF] Kudo | Female migration for marriage: Implications from the land reform in rural Tanzania[END_REF] and probably explains in part the relative lack of interest of the economic literature for female mobility since Thadani and Todaro (1984).

More specifically, this articles links gender-specific migration patterns to the analysis of rural-urban mobility. Regarding internal migrations in sub-Saharan Africa, studies have nuanced the overwhelming focus on rural-to-urban mobility and have highlighted the importance of rural-to-rural migration [START_REF] Beauchemin | Migration and urbanisation in Francophone West Africa: An overview of the recent empirical evidence[END_REF][START_REF] Beauchemin | Rural-urban migration in West Africa: towards a reversal? Migration trends and economic situation in Burkina Faso and Côte d'Ivoire[END_REF][START_REF] Bocquier | African urbanization trends and prospects[END_REF]. Recent research suggest that the urbanization rate in the region has been overstated (Potts, 2012). Rural out-migration has been slowing in the recent decades, and even reversing in some countries [START_REF] Beauchemin | Rural-urban migration in West Africa: towards a reversal? Migration trends and economic situation in Burkina Faso and Côte d'Ivoire[END_REF]Potts, 2009).

Rural-urban migration rates in sub-Saharan Africa are lower than the microeconomic theory would predict given the large and positive income differentials between urban and rural areas [START_REF] Brauw | The role of rural-urban migration in the structural transformation of Sub-Saharan Africa[END_REF]. It is argued here that the observed rural-to-rural patterns in our data have a strong gender component. Female mobility appears to be constrained, more limited geographically, and in a large part subordinate to family reasons. However, the fact that education is found to increase women's likelihood of migrating to urban destinations, suggests possible channels to overcome barriers to female migration.

Third, the current state of the literature allows this paper to provide rare insight into the dynamics of migration and distance within the context of a developing country.

Indeed, recent research has tried to grapple with limitations of migration data aggregated by administrative units [START_REF] Bell | Internal migration data around the world: Assessing contemporary practice[END_REF]. In developed countries, the rationales for migration have been found to differ depending on distance travelled: whereas short-distance mobility is associated with housing and life-cycle motives, long-distance migration is driven by employment motivations [START_REF] Cordey-Hayes | Migration movements and the differential growth of city regions in England and Wales[END_REF][START_REF] Clark | Linking migration and mobility: individual and contextual effects in housing markets in the UK[END_REF][START_REF] Niedomysl | On distance and the spatial dimension in the definition of internal migration[END_REF]. To our knowledge, this article provides the first study using migration distances based on GPS coordinates in sub-Saharan Africa.

Interestingly, our findings are rather consistent with the above categories, but we add to this strand of literature by showing that they are strongly linked to gender-specific migration paradigms. We tend to observe a predominance of short-distance rural-rural marriage-related migrations among women, and more diverse patterns for men with a non-negligible share of long-distance labor-related migration to urban destinations driven by the unrivaled attractiveness of the capital city, Dakar.

Last, together with econometric analysis, the cartographic tools used in this article contribute to highlighting the role of migration hub played by Dakar and provide a vivid illustration of the different types of mobility associated with the declared motives for migrating.

The next section describes the data used. Section 3 presents our empirical methodology. Section 4 presents the econometric results for the determinants of internal migration rural/urban migration and distance traveled, depending on gender, and discusses attrition issues. Finally Section 5 concludes.

Data

The PSF Individual Panel Survey

The data used in this study come from the two waves of the "Poverty and Family Structure" Survey (PSF), conducted in Senegal in 2006-07 for the first wave, and from late 2010 to the beginning of 2012 for the second wave 1 . The sample in the first wave is nationally 1 The survey has been conducted by a team of French researchers and researchers from the National Statistical Agency of Senegal and is described in detail in [START_REF] Devreyer | Pauvreté et Structure Familiale: Pourquoi une nouvelle enquête ?[END_REF]. Momar Sylla and Matar Gueye of the Agence Nationale de la Statistique et de la Démographie of Senegal (ANSD) on the one hand and Philippe De Vreyer (Paris-Dauphine Dauphine, IRD-DIAL), Sylvie Lambert (PSE) and Abla Safir (World Bank) designed the survey. The data have been collected by the ANSD thanks to the representative and made of 1750 households (14,450 individuals), in 150 randomly drawn census districts. All individuals surveyed in the first wave have been tracked, except when abroad, forming an individual panel. The attrition rate between the two waves is 11.6%.

As attrition may result in a great part from internal migration, issues related to attrition are carefully discussed in Section 4.4.

The PSF surveys are particularly suited to the study of internal migration since they provide the exact location of individuals through GPS coordinates in both waves of the panel. Thanks to these coordinates, we calculate Euclidean distances traveled by individuals between the two waves 2 .

The PSF data contain in addition rich information on individual and household sociodemographic characteristics, and on community infrastructures, which allows us to finely document the determinants of internal migration. In particular, consumption data are collected for each household subgroup referred to as a cell. Cells are semi-autonomous consumption units including a cell head and all her dependents (in particular her children, foster children and widowed mother or father). The average number of cells per household is 2.51 3 . We are thus able to account for consumption at both the household and cell levels. We include in all our regressions variables for the household and cell size, and for the relative consumption of the cell. To complement objective wealth indicators and account for relative deprivation as a potential driver of internal migration, we use two distinct questions about the perceived wealth of the household on the one hand, and the community on the other, with 5 modalities each (from "very poor" to "very rich").

Households are classified as "richer" than their community if their self-assessed wealth level is higher than the one reported for their community. 2 While Senegalese geography offers further complexity when it comes to using Euclidean distances, due to the position of the Gambia along the Gambia river, Euclidean measurement is the most relevant and accessible means of computing distances of internal migration [START_REF] Bell | Cross-national comparison of internal migration: issues and measures[END_REF]. Note in addition that most mobility observed from and to the area south of the Gambia, the Casamance, made of the regions of Ziguinchor and Kolda, is connected to the capital city Dakar, as shown in Figure 1. The cities of Dakar and Ziguinchor are connected once more by ferry since 2005, after the dramatic sinking of Le Joola in 2002, and very few travellers choose the land route. The Euclidean distance thus seems to be a relevant proxy for the travel distance even from and to the regions of Senegal south of the Gambia.

3 See Lambert, Ravallion, and van de Walle (2014) for a more detailed description of cell definition.

We used in addition data from a 10% sample of the 2002 Senegalese census to calculate indicators of poverty and inequality4 at the county level, based on 2006 administrative boundaries5 . Figure 6 in Appendix shows the geographic distribution of the computed poverty and inequality statistics at the county level.

Descriptive Statistics

The present analysis focuses on individuals 15 years and older, as the mobility of younger individuals is more likely to be decided on by their parents and subject to specific motives6 . Therefore, the initial database is reduced to a panel of 6,986 individuals (8,636 including attritors, individuals deceased between the two waves and those migrating abroad). To avoid the inherent problems of administrative geography [START_REF] Bell | Internal migration data around the world: Assessing contemporary practice[END_REF], our definition of internal migrants is based on the distance between the two locations calculated from recorded GPS coordinates. We use 5km as a lower bound for internal migration as very short-distance moves may be partly caused by measurement errors.

Moreover, the 5km threshold represents in the Senegalese context a significant enough distance that there are costs attached to this mobility. As a robustness check, other cutoffs where chosen (see Table 6 in Appendix where the definition of internal migrants is based on a 10km cutoff). Based on Euclidean distances, 670 individuals moved of more than 5km between the first and second wave of the survey.

Migrants account for 9.6% of individuals tracked in the panel. Descriptive statistics in the Appendix present characteristics of individuals and of their household in the first wave of the survey, which are relevant for understanding the determinants of migration between the two survey waves. When including all types of migration (internal and international), internal migration accounts for 69% of migrants, making it a significant phenomenon to study. As appears in Table 4, migrants are more likely to be women (58.6% compared to 55.3% for non-migrants), they tend to be better educated (29.1% have a secondary education or higher compared to 19% among non-migrants) and are younger (66.5% are under 30 compared to 46.3% for non-migrants).

Regarding the geography of internal migrations, the data reveal the overwhelming polarity and attractiveness of Dakar. Indeed 16.1% of internal migrants in our data come from Dakar, while 21% move to Dakar between the two survey waves (excluding Intra-Dakar mobility). In ). As a robustness check, we exclude intra-Dakar migrants from our sample of internal migrants, since mobility within the community of Dakar, even though on a distance larger than 5km, might not be considered migration.

Table 5 in Appendix focuses on rural/urban migratory dynamics and confirms the intensity of migration to urban centers, with 70% of internal migrants moving to urban settings. Particularly notable is the intensity of migration from urban-to-urban settings which accounts for 77% of migrations for individuals originating in urban areas. This should be in part nuanced by the intensity of mobility within the region of Dakar, which accounts for 41% of all urban-to-urban mobility. This intensity of intra-Dakar mobility finds parallels with part of the argument made by [START_REF] Beauchemin | Migration and urbanisation in Francophone West Africa: An overview of the recent empirical evidence[END_REF] on migration and urbanization whereby intra-urban mobility (and its peri-urban spaces, which are Pikine and Guédiawaye for Dakar) better explains urban expansion than inmigration initially. Figure 3 shows the distribution of reasons for migration across distance travelled and reveals a striking contrast with regards to reasons for moving between women and men. Regardless of distance, 40 to 60% women's mobility is explained by marriage or return to spousal home. Employment and education are marginal migration motives for women and appear only for medium to long distances. By contrast, except for very short distances (under 50km), 40 to 66% of male migration is explained by either education or employment.

3 Empirical approach

Empirical models

In line with the individual models of migration derived from Todaro (1997) explaining migration decision by earning differentials we explore the role of individual variables such as gender, age, education or socio-professional category in the migration decision. We account for the contributions of the literature initiated by Stark and Bloom (1985) and Rosenzweig and Stark (1989) that emphasized the household dimension of the migration decision by considering individuals' relative position in the household. We control in particular for the relationship to the household head and for the birth rank among siblings as previous research in the case of Senegal has shown that elders are more likely to migrate as they are expected to send more remittances [START_REF] Chort | Selection into Migration within a Household Model: Evidence from Senegal[END_REF]. In addition, we investigate the question of relative deprivation as a potential driver of migration (Stark, 1984;Stark and Taylor, 1989) at three different levels. At the household level first, we exploit the rich data on consumption disaggregated at the cell (household subgroup) level to proxy for the relative economic status and/or bargaining power within the household.

Second, we use subjective data on household wealth compared to the perceived average wealth of the community. Finally, we explore the impact of inequality at the county level, as, according to Stark (1984), we should observe more migration where the distribution of income is more unequal. Building on the literature focusing on the impact of the quality of amenities on migration [START_REF] Dustmann | Out-migration, wealth constraints, and the quality of local amenities[END_REF], we control for the availability of education and health services in the community.

We estimate a probit model for migration decision :

IntM igrant * i = α + β X i + i (1)
where IntM igrant * i is a latent variable only observed as:

IntM igrant i = 1 {IntM igrant * i >0} (2)
IntM igrant i is a dummy variable equal to one if individual i has migrated internally between the two survey waves. More precisely, internal migrants are defined as individuals surveyed in the second wave at a location distant of more than 5km from their initial location. As robustness checks, we use a 10km threshold instead and we exclude mobilities within the capital city of Dakar (see Tables 6 and7 in Appendix). Note that for lack of exhaustive retrospective information on individual migration trajectories, we cannot account for temporary mobility that occurred between the two survey waves, i.e.

individuals who migrated and settled back in their household of origin. X i is a set of individual, household, community and county (département) characteristics. Individual variables include gender, age, education, ethnicity, dummies for having been fostered before the age of 15 and for first-borns, relationship to the household head, and socioprofessional status. Household controls are the size of the household, a consumption index per adult equivalent, the size of the cell, the ratio between cell consumption and household consumption and a measure of self-reported wealth within the community.

Community determinants include controls for the environment (urban or rural) and public services (public hospital, primary and secondary schools). Finally, two variables are defined at the county (département) level: a measure of poverty (headcount) and a measure of inequality (Gini index). i is an individual specific error term. We estimate our model on the pooled sample (men and women) and separately for each gender, as we expect migration determinants to vary across gender.

Second, on the sample of migrants, we investigate the determinants of distance travelled by estimating the following equation with OLS:

LnDIST i,w1-w2 = γ + δ X i + ν i (3)
where LnDIST i,w1-w2 denotes the log of the Euclidian distance between locations of individual at waves 1 and 2, computed based on the GPS coordinates collected by the surveyors. X i is the same set of individual, household, community and county characteristics than in equation 1 and ν i is an error term.

Finally, we estimate a multinomial logit model to investigate the issue of rural/urban migrations. Instead of considering the binary decision to migrate or stay, we model the three-option choice to migrate to an urban area, to a rural area, or stay.

4 Empirical findings

Determinants of migration

Table 1 presents the estimation results of a Probit model for internal migration decision on the whole sample (columns 1 and 2), and separately for women (column 3 and 4) and men (columns 5 and 6). According to our definition of internal migrants, the dependent variable is a dummy equal to one for individuals who were living in the second survey wave in a household distant of more than 5km from their household in wave 1. In addition to individual and household determinants of migration, specifications shown in columns 2, 4 and 6 include migration push-factors at the community and county level.

As a robustness check, we used an alternative threshold of 10km for the definition of migrants. The results are very similar, as shown in Table 6 in Appendix. Moreover, to avoid mixing intra-urban relocation and internal migration, we replicated the analysis excluding individuals moving within the capital city of Dakar, irrespective of the distance.

Results are shown in Table 7 in Appendix.

Since the decision to migrate within the country and abroad are probably interconnected, we estimated a multinomial logit model for migration with three alternatives: stay (the reference), migrate internally, or migrate abroad. Results are shown in Table 13 and are remarkably close to those obtained in our main specifications, with only marginal differences in the coefficients on the ethnicity dummies.

As mentioned above, attrition is a major concern as we expect internal migration to be the major cause of attrition between the two survey waves. We provide regression results including attrition in Table 12 and discuss further attrition issues in Section 4.4. What appears evident from Table 1, Column 1 is the importance of a gendered component to internal migration: women are more likely to be internal migrants than men.

As discussed below in Section 4.4, this highly feminized migration dynamic may be nuanced as models with attrition reveal that men are more likely to have been lost between the two survey waves, although not all of them can be considered internal migrants.

A few characteristics are common to male and female migrants, in particular those measured at the household, department and county level. First, as expected, migrants tend to be younger than stayers. The effect is found to be significant for women only, most probably caused by marriage as one of the main motive of female migration. Second, regardless of gender, being a child or sibling of the household head is associated with a significantly greater probability of migrating. Third, household income, proxied by consumption per adult equivalent, tends to be positively correlated with the probability of migrating of both men and women, although the coefficient on the consumption variable is larger and significant only for men. Once controlling for the characteristics of the environment, i.e. living in the capital city, in another city or in a rural area, and poverty and inequality at the county level, we find no significant impact of amenities at the community level at conventional levels. Note however that most coefficients are negative and that the coefficient on the dummy for a public hospital is significant at the 10% level for men when excluding intra-Dakar migration (Table 7, column 6). Interestingly, this result is consistent with [START_REF] Dustmann | Out-migration, wealth constraints, and the quality of local amenities[END_REF] who analyze emigration intentions and find a negative correlation between contentment with local amenities and intention to migrate in sub-Saharan Africa. Finally, at first glance county characteristics seem to have comparable impacts on men and women's migration: poverty has a positive effect on migration, though twice larger for women than for men, and inequality tends to decrease migration. However, when excluding intra-Dakar migration, we find a positive effect of poverty on female migration only, suggesting that poverty at the regional level is an important "push-factor" for women.However, we do not know whether they migrated in a less poor area, as we do not have enough variation in the poverty rate at destination due to the high share of internal migrants going to Dakar 7 . This finding is also consistent with the persistence of traditional practices of marriage-related female migration in the poorest and most remote areas of the country. This issue is further discussed in the following sections.

Separate regressions for men and women reveal numerous differences in the individual migration determinants of the two groups. Having been fostered is associated with a significantly higher probability of internal migration for men only. This finding is in line with the literature on fostering as a household strategy aimed at increasing children's social mobility which could be associated with a greater geographic mobility in adulthood.

The difference across genders is linked to the different motives behind boys and girls'

fostering, as women are more likely to be fostered into households in which they will be married [START_REF] Beck | Child fostering in Senegal[END_REF].

Ethnicity is found to be correlated with female migration only. Women belonging to Diola ethnic group and, to a lesser extent, to the Serere ethnic group are more likely to migrate than members of the Senegalese largest Wolof ethnic group. This finds parallels in the work of [START_REF] Brockerhoff | Demographic and socioeconomic determinants of female rural to urban migration in Sub-Saharan Africa[END_REF] documenting mobility by Serere and Diola women to urban regions for domestic work.

As for education, we find that men with at least some primary education are more likely to become internal migrants than those with no education at all (Table 1, Column 5-6), while for women, no significant differences in migration propensities are observed depending on educational level.

Migration distance

7 Although there is variation in the poverty rate within Dakar between poor areas like Guédiawaye and rich ones such as the Almadies, the 10% extract of the 2002 census that we could exploit does not allow us to construct poverty measure at a finer level of disaggregation than the county level (département). The same limitations applies to our county-level inequality measure which is included as a "push" factor only. Having evaluated selection into migration, another crucial element of this analysis and the originality of this paper is to evaluate the determinants of migration across distance.

Table 2 shows the results of OLS regressions using the logarithm of distance as dependent variable, on the sample of internal migrants, i.e. individuals who moved of more than 5km, and separately for female and male migrants. Table 8, in Appendix, presents a similar analysis but excludes intra-Dakar migrants, regardless of distance travelled, from the regression samples. As for men, we find a positive impact of household wealth proxied by consumption per adult equivalent on migration distance which is robust to the exclusion of intra-Dakar migration. This result is consistent with the existence of migration costs, but also with education as one of the primary reason for male migration that implies moving to the capital city of Dakar and that only richer household can afford. Men with secondary or higher education are found to move less far, which is very likely explained by higher educational levels in regions close to the capital city where employment opportunities are concentrated.

A common feature of male and female migrations is the positive relationship between inequality in the county of origin and distance travelled. This finding is in line with the theoretical framework developed by Stark (1984) and with relative deprivation as a driver of migration, as individuals living in areas with a higher income inequality may move further to escape relative poverty. Such result is also linked to the geography of Senegal and the attractiveness of Dakar. As illustrated by Figure 1 , a majority of individual trajectories converge from all regions towards Dakar. Moreover, the most remote regions in the South-East of the country are also characterized by the largest levels of inequality. By contrast, poverty at the county level is not significantly correlated with migration distance. However, the coefficient on the poverty headcount becomes significant for women only, when excluding intra-Dakar migrants (see Table 8, column 4). Note that the negative effect of Dakar location (as opposed to rural and other urban areas) on migration distance is fully explained by intra-Dakar migration, as the effect vanishes and even reverses for women when excluding intra-Dakar relocation. In order to complement our analysis of the determinants of migration distance, we take into account the rural-urban dimension of internal migration, related to gender. Table 3 presents the results of a multinomial logit models where migration is decomposed into rural and urban destinations, the reference being not migrating. Table 9 in Appendix presents the same regressions excluding intra-Dakar movers from the definition of migrants. What appears clear from Column 1 is that women are more likely than men to move to rural areas. This is especially true of first-born women, consistent with marriagedriven migration [START_REF] Herrera | Determinants of Internal Migration among Senegalese Youth[END_REF]Quisumbing and McNiven, 2010). Educational achievement has opposite effects on the decision to move to an urban or rural destination (Table 3, Column 1). Those with primary or secondary education are more likely to move to urban areas and less likely to move to rural areas than non-educated individuals. This finds parallels in works on internal migration in other countries. [START_REF] Ackah | Internal migration in Ghana: determinants and welfare impacts[END_REF] notably find for Ghana that individuals are more likely to move to urban settings from areas where infrastructure is lacking. [START_REF] Msigwa | Determinants of internal migration in Tanzania[END_REF] observe similar trends for Tanzania with younger, educated males moving to urban settings. While they do not use personal education, Herrera and Sahn (2013) find for Senegal that father's education has a positive influence especially on female migration to urban settings. The correlation between education and rural-urban migration is particularly significant for women -positive with migration to urban areas, negative with migration to rural areas, which may reveal a rift in opportunities and rationales for moving for women depending on educational achievement. Interestingly, the effect of education is robust to the exclusion of intra-Dakar migration for women, while it looses its significance for men.

Rural-urban migration patterns

Relationship to the household head highlights different trajectories of sons and daughters: while male children or siblings of the household head are more likely to migrate to urban centers, female children and siblings have a higher probability to migrate to rural areas. Furthermore, certain socio-professional categories are more likely to select migration to urban areas rather than rural areas: this is clear for independents, salaried workers, students and the unemployed. Cities remain the main centers for employment and ed-ucation [START_REF] Beauchemin | Migration and urbanisation in Francophone West Africa: An overview of the recent empirical evidence[END_REF]. Unsurprisingly, individuals from wealthier households tend to migrate to urban areas. Interestingly, subjective relative household wealth is related in a different way to male and female migration. Men in self-perceived richer households have a lower probability to move to rural areas, while women in relatively poor households are more likely to migrate to urban settings. Our results for women are consistent with relative deprivation as a driver of migration decisions, but such an assumption is not supported by empirical evidence for men. The effect of indices measured at the county level confirm that higher poverty rate increase female migration to both destinations.

Excluding intra-Dakar mobility, we find that being born in a rural area has a positive effect on the probability of migrating to a rural area which is found significant for women only (Table 9, column 4). Additional specifications decomposing migration by both destination and origin provide consistent evidence that women are more likely to experience rural-to-rural moves than men (results not shown, available upon request).

Treatment of attrition

A crucial issue when studying migration using panel data is linked to attrition. Individuals who were not found in the second survey wave are presumably in large part individuals who left their household of origin, and maybe moved far away enough that surveyors were not able to find them in their community of origin. It could thus be argued that attritors should be treated as migrants. However, as we focus on internal migration such a solution tends to overinflate both the importance of internal migration and the consequences of attrition. Indeed, a non-negligible share of attritors is expected to fall outside the scope of our analysis: first, whereas it seems doubtless that individuals who could not be found in their household of origin have moved, some are likely to have migrated abroad.

Second, even when excluding international migrants, attritors do not exactly match our definition of migrants, as we consider a lower bound of 5km as the minimum distance associated with mobility costs high enough to discriminate migration from mere housing mobility. Indeed, a significant share of attritors may have moved relatively close to their household of origin and still be lost, especially in Dakar. Note that 57% of attrition concerns individuals living in Dakar, where individuals may not be as easily traced as in smaller towns or rural communities. Furthermore we observe a high mobility within Dakar, which supports our assumption that among attritors who were still alive and remained in Senegal, a non negligible share falls out of our definition of internal migrants.

Tables 10 and 11 in Appendix compare the observed characteristics of attritors to those of four distinct groups: internal migrants (i.e. individuals who moved of more than 5km), deceased individuals, international migrants and movers of less than 5km. Columns 6 to 9 test the equality of the mean or percentages for the different variables used in the analysis. The tests suggest that attritors have characteristics which are closer on average to those of international migrants than to any other group. This is particularly true with regard to education, socio-professional category, household measured and self-perceived wealth, and community infrastructures, for which no significant difference is observed between individuals who could not be tracked and international migrants. This observation, although it cannot be used as a proof, suggests that international migration is probably a major driver of attrition.

In order to analyze the sensitivity of our results to attrition, we estimated a probit model for internal migration treating attritors as internal migrants. For the above stated reasons, considering individuals who could not be tracked as internal migrants leads us to overinflate the internal migrant category, since, as discussed above, attrition is also probably caused in part by death, international migration and short-distance housing mobility. Results are presented in Table 12, columns 1 to 3 for the total sample, and separately for women and men, together with the results of probit models for the determinants of attrition. First, the coefficient on the male dummy in column 1 is not significant when treating attrition as internal migration. Indeed, men are more likely than women to be lost between the two survey rounds. This finding confirms that female migration is less independent than male migration, as women are more easily tracked, meaning that they may be less likely to cut-off links with their origin household when moving. In addition, the share of attrition due to the loss of the entire household is lower for women (45.9%) than for men (52.3%). The difference is partly due to the frequent loss of urban one-person households characterized by a higher mobility and a lower insertion in local networks. One-person households lost are almost exclusively male as women living alone is a very marginal phenomenon: 43 male individuals living alone were lost, representing 15.2% of male attrition, compared to 6 women only (2.6% of female attrition). However, apart from the different gender composition of the attrited and migrant population, most observations driven from Table 1 are unchallenged when treating attrition as internal migration. When looking more specifically at the determinants of attrition, we find that individuals with low levels of education, weak ties to the head of the household and living in Dakar are more likely to have been lost. For women, attrition is very likely driven in part by the high mobility of young salaried domestic workers (maids or petites bonnes), documented in the Malian case by [START_REF] Lesclingand | Migrations des jeunes filles au Mali: exploitation ou émancipation?[END_REF]. Such an interpretation is supported by the positive and significant coefficient on the salaried worker dummy in the female regression (column 5) and the positive correlation with household income as only relatively wealthy households can afford to employ domestic workers. By contrast, male attrition may be caused in part by international migration, as male spouses of the head are more likely to be lost, as well as individuals from wealthier households. This result is consistent with the descriptive statistics showing that attritors and international migrants share many common features (10 and 11). In sum, although male attrition is more frequently observed, it may have little impact on our analysis, as it seems to be driven in part by international migration. On the other hand, female attrition is less frequent but seems to be specific to vulnerable populations with low-level and precarious jobs. Our study probably misses part of the phenomenon of female migration by losing track of these highly mobile urban populations living at the periphery of their household.

However, to mitigate this issue, it is important to note that such mobility could be called secondary in the sense that in order to get employed, these women had already migrated from their household of origin with which they may have kept links. The primary mobility of this specific population should thus appear in our data.

Attrition may also be an issue for the analysis of migration distance. Indeed, as attrition is partly caused by internal migration, it may be correlated with migration distance.

The sign of the correlation is however ambiguous: individuals migrating further away may be less easily tracked, but short-distance urban mobility may generate more attrition due to the weaker neighbourhood networks. Our estimates of the determinants of migration distance may thus be biased by selective attrition. However, the distance travelled by those among attritors who are indeed internal migrants is unknown. The above robustness checks consisting in pooling attritors and internal migrants in the analysis of the probability of migrating is not applicable for migration distance. In order to investigate this issue we thus choose another approach. Following Senne (2014), we estimate a two-step [START_REF] Heckman | Sample Selection Bias as a Specification Error[END_REF] selection model, using dummies for second-wave fieldwork controller in charge of first recontacting households at their first-wave location as excluded instruments8 . Indeed, the success of the tracking of individuals who had left their initial household heavily relied on the accuracy of information collected among other household members found at first-wave location of the household, or among neighbours if the whole household had moved. We expect individual characteristics of fieldwork controllers to have an impact on tracking outcomes, and thus on attrition, while being uncorrelated with migration distance. Second-stage estimates are reported in Table 13 in Appendix.

The comparison of results shown in Tables 2 and13 suggests that the bias due to attrition is small, as the sign, size and significance of coefficients in both tables are very close.

Conclusion

This article studies the determinants of internal migration using rich individual panel survey data collected in Senegal in 2006-07 and 2010-12. The tracking of all individuals who remained in Senegal allow us to identify and map migrations between the two survey waves using the GPS coordinates at both dates. These features of our data are unique in this region of the world and allow us to make a significant contribution to the literature on internal migration in sub-Saharan Africa. Using distance rather than administrative boundaries has the advantage of providing us with a definition of migration which is less arbitrary and homogeneous across regions.

The empirical analysis reveals clear differences between women and men. Women are more likely than men to have migrated between the two survey rounds, however, they tend to migrate over shorter distances. The decomposition of the migration decision in rural and urban destinations confirms and complements this study by showing that women are more likely than men to migrate to rural areas, especially when originating from rural areas. Such moves are related to the different motivations behind male and female migration. The primary reason for migrating for women in our sample is marriage, whatever the distance travelled. By contrast, labor and education are the most cited motives behind male migration.

Our findings reveal surprisingly little change since the pioneering works on female migration dating back from the early 1990s [START_REF] Chant | Gender & migration in developing countries[END_REF]. Female migration still depends in a large part on family events and has few connections with labor market participation, contrary to male migration. For this reason, women are over-represented in rural-to-rural flows while rural-to-urban migration is more commonly observed for men.

These observations echo the conclusions of De Brauw, Mueller, and Lee (2014) noting the surprisingly low rural-urban flows in sub-Saharan Africa given the rural-income wage gap. In the light of our results, policies aimed at encouraging rural to urban migration that would target women would presumably have a stronger impact, as women are still largely marginalized from labor-related moves. In line with [START_REF] Brauw | The role of rural-urban migration in the structural transformation of Sub-Saharan Africa[END_REF], the present study shows that education increases the likelihood of migrating to urban areas especially for women, suggesting an efficient channel for promoting women's access to independent migration. Reasons for Migration (Women) 44 38 2.9 2.9 2.9 5.9 2.9 , 2006-2007 and 2010-2012 Table 7: Probit models of internal migration decision with intra-Dakar movers treated as non-migrants (marginal effects)

28
All Women Men (1) (2)
(3) (4)

(5)

(2)

(

(5)

(6) (7) (8) (9) Migrant Deceased Abroad Moved Lost t/χ 2 t/χ 2 t/χ 2 t/χ 2
(1)-( 5)

(2)-( 5)

(3)-( 5 All means are calculated at the individual level, to make the comparison between the different groups easier as households may include individuals in several categories. Large households thus tend to be over-represented in the reporting of descriptive statistics for household variables. , 2006-2007 and 2010-2012 Table 14: Multinomial logit models of internal and international migration decision (marginal effects) , 2006-2007 and 2010-2012

  who focus only on Senegalese youth (21-35 year old) and measure internal migration based on retrospective data collected in 2003.

  funding of the IDRC (International Development Research Center), INRA Paris and CEPREMAP.

Figure 1

 1 Figure 1 represents individual mobilities between the two survey waves, based on GPS coordinates. Different colors materialize the different regions of origin while dots represent destinations. The attractiveness of Dakar is illustrated by the numerous lines converging towards the capital city. Interestingly, Dakar is strongly connected to all Senegalese

Figure 1 :

 1 Figure 1: Internal migrations in Senegal, by region of origin

Figure 3 :

 3 Figure 3: Reasons for Migration

  and Family Structure Survey, 2006-2007 and 2010[START_REF] Ackah | Internal migration in Ghana: determinants and welfare impacts[END_REF]

  variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey, 2006-2007 and 2010-2012Table 8: Determinants of migration distance -OLS estimation (sample: adult migrants (+15 years) > 5km excluding intravariables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey, 2006-2007 and 2010-2012

  and Family Structure Survey, 2006-2007 and 2010[START_REF] Ackah | Internal migration in Ghana: determinants and welfare impacts[END_REF] †Consumption per adult equivalent in thousands XOF (619 XOF ≈ 1 USD)

  and Family Structure Survey, 2006-2007 and 2010[START_REF] Ackah | Internal migration in Ghana: determinants and welfare impacts[END_REF] †Consumption per adult equivalent in thousands XOF (619 XOF ≈ 1 USD)

α

  Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2(World Bank, 2009) Source: Poverty and Family StructureSurvey, 2006Survey, -2007Survey, and 2010Survey, -2012

Figure

  Figure 4: Urban/Rural Migration

  addition, intra-Dakar mobility (of more than 5km) represents 17.3% of internal migration. Overall, internal migrants going to or from Dakar represent 37.2%

of all migrants (54.4% including intra-Dakar mobility) while the Dakar metropolitan area accounts for 20% of the Senegalese population in 2002 (ANSD (Agence Nationale de la Statistique et de la Démographie), 2006

Table 1 :

 1 Probit models of internal migration decision (marginal effects)

				(0.002)	(0.000)	(0.014)	(0.011)	(0.016)	(0.013)	(0.023)	(0.017)		(0.019)	(0.020)	(0.015)	(0.016)	(0.016)	(0.020)	(0.020)	(0.024)	(0.024)	(0.021)	(0.019)		(0.007)	(0.001)	(0.003)	(0.030)	(0.016)	(0.013)		(0.018)	(0.024)	(0.015)	(0.004)	(0.005)		(0.069)	(0.139)
	Men	(6)		(0.002) 0.001	(0.000) -0.000	(0.014) 0.025 *	(0.011) -0.006	(0.016) 0.016	(0.013) -0.012	(0.023) 0.018	(0.016) -0.002		(0.019) 0.056 * * *	(0.020) 0.113 * * *	(0.015) 0.033 * *	(0.016) 0.054 * * *	(0.016) -0.004	(0.020) 0.030	(0.019) 0.030	(0.024) -0.001	(0.024) 0.041 *	(0.021) 0.017	(0.019) 0.016		(0.007) 0.019 * * *	(0.001) -0.001	(0.003) -0.003	(0.030) 0.022	-0.018	0.009		(0.014) -0.021	(0.016) 0.018	-0.023	-0.007	-0.002		0.114 *	-0.268 *	3043
		(5)		(0.002) 0.001	(0.000) -0.000	(0.014) 0.026 *	(0.010) -0.005	(0.016) 0.022	(0.013) -0.013	(0.021) 0.008	(0.015) -0.005	(0.022)	(0.024) 0.058 * * *	(0.024) 0.110 * * *	(0.014) 0.031 * *	(0.017) 0.052 * * *	(0.015) -0.001	(0.024) 0.031	(0.025) 0.029	(0.023) 0.002	(0.027) 0.042 *	(0.019) 0.009	(0.020) 0.017		(0.007) 0.016 * *	(0.001) -0.001	(0.003) -0.002	(0.029) 0.012	(0.014)	(0.012)		(0.017) 0.018	(0.022) 0.076 * * *	(0.014)	(0.004)	(0.004)		(0.065)	(0.125)	3043
	Women	(4)		(0.002) -0.003 *	(0.000) 0.000	(0.014) 0.014	(0.010) 0.015	(0.016) 0.018	(0.012) 0.002	(0.021) 0.061 * * *	(0.015) 0.026 *	(0.022) -0.029	(0.024) 0.045 *	(0.024) 0.034	(0.013) -0.009	(0.017) 0.011	(0.015) 0.004	(0.024) -0.012	(0.025) -0.001	(0.023) 0.029	(0.027) 0.025	(0.019) 0.021	(0.019) 0.048 * *		(0.007) 0.011	(0.001) -0.002	(0.003) -0.001	(0.030) 0.016	0.011	0.012		(0.014) -0.065 * * *	(0.014) -0.046 * *	0.018	-0.003	-0.005		0.230 * * *	-0.229 *	3842
		(3)
			(0.008)	(0.001) -0.003 *	(0.000) 0.000	(0.010) 0.015	(0.008) 0.016	(0.011) 0.023	(0.009) 0.005	(0.016) 0.054 * *	(0.011) 0.027 *	(0.015) -0.026	(0.014) 0.046 *	(0.015) 0.033	(0.010) -0.010	(0.011) 0.005	(0.011) 0.004	(0.016) -0.020	(0.016) -0.011	(0.017) 0.030	(0.018) 0.020	(0.014) 0.010	(0.014) 0.042 * *		(0.005) 0.007	(0.001) -0.002	(0.002) -0.002	(0.021) 0.015	(0.010)	(0.009)		(0.013) -0.021	(0.016) 0.007	(0.010)	(0.003)	(0.003)		(0.047)	(0.093)	3842
	All	(2)	(0.008) -0.025 * * *	(0.001) -0.001	(0.000) 0.000	(0.010) 0.020 * *	(0.008) 0.006	(0.011) 0.018	(0.009) -0.005	(0.016) 0.041 * * *	(0.011) 0.013	(0.015) -0.017	(0.014) 0.051 * * *	(0.015) 0.067 * * *	(0.010) 0.010	(0.011) 0.029 * *	(0.011) -0.002	(0.016) 0.014	(0.015) 0.020	(0.017) 0.017	(0.018) 0.037 * *	(0.013) 0.019	(0.014) 0.035 * * *		(0.005) 0.014 * * *	(0.001) -0.001	(0.002) -0.002	(0.021) 0.021	-0.001	0.011		(0.010) -0.046 * * *	(0.010) -0.023	-0.002	-0.004	-0.004		0.184 * * *	-0.232 * *	6906
		(1)	-0.025 * * *	-0.002	0.000	0.021 * *	0.007	0.022 *	-0.004	0.032 * *	0.013	-0.014	0.052 * * *	0.066 * * *	0.008	0.026 * *	-0.000	0.009	0.016	0.020	0.035 *	0.012	0.034 * *		0.010 * *	-0.001 *	-0.002	0.014				-0.002	0.036 * * *							6906
		Individual Characteristics	Male	Age in years	Age squared	Fostered	First-born	Serere	Poular	Diola	Other Ethnic Group	Spouse/Parent of the Head	Child/Sibling of the Head	Other/Non-Relatives	Primary Education	Secondary Education or University	Quranic Education	Independent/Employer	Salaried Worker/Intern/Trainee	Family Worker	Student	Inactive/Unemployed	Missing Employment Category	Household Characteristics	Consumption Index (adult eq.)	Household Size	Household Cell Size	Cell/Household Expenditure	Self-Reported Richer than Community	Self-Reported Poorer than Community	Community Characteristics	Other cities	Rural	Public Hospital	Nb Public Primary Schools	Nb Public Secondary Schools	County (Département) Characteristics †	Headcount Poverty	Gini Index	Observations	Standard errors in parentheses,

* p < 0.10, * * p < 0.05, * * * p < 0.01 α Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey

, 2006-2007 and 2010-2012

Table 2 :

 2 Determinants of migration distance -OLS estimation (sample: adult migrants (+15 years) > 5km)

				(0.034)	(0.000)	(0.203)	(0.165)	(0.246)	(0.213)	(0.337)	(0.277)		(0.335)	(0.348)	(0.230)	(0.246)	(0.269)	(0.317)	(0.305)	(0.376)	(0.334)	(0.329)	(0.299)		(0.099)	(0.019)	(0.042)	(0.414)	(0.262)	(0.184)		(0.286)	(0.339)	(0.258)	(0.072)	(0.076)		(1.093)	(2.271)	(1.737)
	Men	(6)		(0.034) -0.028	(0.000) 0.000	(0.209) -0.424 * *	(0.168) 0.061	(0.251) -0.140	(0.208) 0.191	(0.341) 0.040	(0.271) -0.166		(0.343) 0.275	(0.356) 0.333	(0.236) -0.302	(0.253) -0.787 * * *	(0.277) 0.064	(0.325) 0.445	(0.310) 0.401	(0.387) 0.632 *	(0.345) 0.678 * *	(0.330) 0.597 *	(0.305) 0.703 * *		(0.100) 0.144	(0.019) 0.028	(0.042) -0.030	(0.421) 1.029 * *	-0.465 *	0.095		(0.226) 1.658 * * *	(0.254) 1.625 * * *	0.212	0.061	0.066		-0.983	7.554 * * *	(1.054) -1.355	270	0.358
		(5)		-0.038	0.000	-0.352 *	0.022	-0.307	0.337	0.436	0.029		0.223	0.281	-0.289	-0.737 * * *	0.094	0.517	0.353	0.514	0.649 *	0.601 *	0.815 * * *		0.208 * *	0.037 *	-0.051	1.288 * * *				1.279 * * *	0.974 * * *							1.674	270	0.284
				(0.026)	(0.000)	(0.200)	(0.153)	(0.227)	(0.188)	(0.309)	(0.229)	(0.371)	(0.391)	(0.386)	(0.195)	(0.236)	(0.225)	(0.406)	(0.377)	(0.335)	(0.375)	(0.282)	(0.287)		(0.102)	(0.018)	(0.044)	(0.419)	(0.209)	(0.179)		(0.255)	(0.325)	(0.231)	(0.059)	(0.065)		(0.920)	(1.864)	(1.400)
	Women	(4)		(0.026) 0.015	(0.000) -0.000	(0.201) -0.088	(0.156) -0.290 *	(0.233) 0.227	(0.185) 0.093	(0.306) 0.139	(0.226) 0.123	(0.378) -0.077	(0.397) 0.246	(0.393) 0.342	(0.196) -0.412 * *	(0.239) -0.288	(0.228) -0.082	(0.408) -0.028	(0.382) 0.633 *	(0.343) 0.095	(0.380) 0.472	(0.281) 0.246	(0.290) 0.468		(0.102) -0.061	(0.018) 0.014	(0.045) -0.102 * *	(0.426) 0.473	0.134	0.009		(0.207) 0.816 * * *	(0.211) 0.027	-0.296	0.014	0.082		1.028	8.185 * * *	(1.032) -0.531	385	0.179
		(3)	(0.118)	(0.020) 0.027	(0.000) -0.000	(0.140) -0.054	(0.112) -0.312 * *	(0.165) 0.194	(0.140) 0.247	(0.222) 0.282	(0.174) 0.388 *	(0.248) -0.264	(0.238) 0.137	(0.240) 0.287	(0.145) -0.293	(0.166) -0.159	(0.168) -0.132	(0.250) -0.076	(0.236) 0.479	(0.247) 0.053	(0.249) 0.487	(0.205) 0.189	(0.205) 0.376		(0.070) -0.050	(0.013) 0.011	(0.030) -0.097 * *	(0.285) 0.393	(0.159)	(0.126)		(0.188) 0.720 * * *	(0.231) 0.131	(0.168)	(0.045)	(0.049)		(0.685)	(1.399)	(1.032) 3.328 * * *	385	0.116
	All	(2)	(0.121) 0.450 * * *	(0.020) -0.004	(0.000) 0.000	(0.144) -0.215	(0.115) -0.142	(0.170) 0.079	(0.138) 0.146	(0.223) 0.096	(0.173) -0.001	(0.255) 0.091	(0.244) 0.426 *	(0.247) 0.453 *	(0.148) -0.383 * * *	(0.171) -0.645 * * *	(0.172) -0.010	(0.257) 0.250	(0.241) 0.319	(0.255) 0.258	(0.257) 0.615 * *	(0.206) 0.329	(0.209) 0.597 * * *		(0.071) 0.062	(0.013) 0.022 *	(0.031) -0.073 * *	(0.294) 0.799 * * *	-0.067	0.073		(0.153) 1.203 * * *	(0.162) 0.784 * * *	-0.122	0.029	0.105 * *		0.037	7.910 * * *	(0.711) -1.450	655	0.212
		(1)	0.416 * * *	0.002	-0.000	-0.163	-0.162	-0.040	0.265 *	0.345	0.222	-0.034	0.335	0.421 *	-0.281 *	-0.523 * * *	-0.015	0.241	0.216	0.223	0.571 * *	0.341 *	0.570 * * *		0.111	0.025 *	-0.078 * *	0.853 * * *				0.979 * * *	0.503 * * *							1.920 * * *	655	0.146
		Individual Characteristics	Male	Age in years	Age squared	Fostered	First-born	Serere	Poular	Diola	Other ethnic group	Spouse/Parent of the Head	Child/Sibling of the Head	Other/Non-Relatives	Primary Education	Secondary Education or University	Quranic Education	Independent/Employer	Salaried Worker/Intern/Trainee	Family Worker	Student	Inactive/Unemployed	Missing Employment Category	Household Characteristics	Consumption Index (adult eq.)	Household Size	Household Cell Size	Cell/Household Expenditure	Self-Reported Richer than Community	Self-Reported Poorer than Community	Community Characteristics	Other cities	Rural	Public Hospital	Nb Public Primary Schools	Nb Public Secondary Schools	County (Département) Characteristics †	Headcount Poverty	Gini Index	Constant	Observations	R 2	Standard errors in parentheses,

* p < 0.10, * * p < 0.05, * * * p < 0.01 Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey

, 2006-2007 and 2010-2012

Table 2

 2 confirms the gendered nature of migration patterns as the distance travelled by men is around 45% greater than that travelled by women. Separate regressions by gender

reveal different determinants of migration distance for men and women. Women are found to migrate less far when they are the eldest of their siblings, consistent with gender roles in the Senegalese society. Indeed, eldest daughters have an important parental role for their youngest siblings. In addition, since marriage in Senegal is accompanied by a bridewealth payment to the wife's family, the marriage of the eldest daughter is expected to provide their younger brothers with the resources to get married. This financial dependency of the household on the marriage of the eldest daughter which is common to many other African societies

(Trinitapoli, Yeatman, and Fledderjohann, 2014;[START_REF] Horne | The shadow of indebtedness: Bridewealth and norms constraining female reproductive autonomy[END_REF]

may explain in part that eldest daughters move less far, as their household of origin seeks to maintain close links with her.

Table 3 :

 3 Multinomial Logit models of rural/urban migration decision (marginal effects) Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey, 2006-2007 and 2010-2012

	(3)	Men	Urban Dest. Rural Dest.		0.001 (0.002) (0.001) -0.000	-0.000 (0.000) (0.000) -0.000	0.018 (0.012) (0.007) 0.004	-0.005 (0.010) (0.005) -0.001	-0.062 * * * (0.016) (0.013) -0.013	-0.030 * * (0.015) (0.010) 0.031 * * *	-0.026 (0.038) (0.022) 0.015	0.007 (0.013) (0.009) 0.007	-0.018 (0.012) (0.007) 0.008	-0.015 (0.021) (0.010) 0.026 * *	-0.018 (0.016) (0.008) 0.012	-0.645 (23.431) (12.650) -0.172	0.048 * * * (0.017) (0.011) 0.016	0.071 * * * (0.018) (0.011) 0.036 * * *	0.040 * * * (0.014) (0.008) 0.001	0.051 * * * (0.015) (0.008) 0.008	0.000 (0.016) (0.008) -0.006	0.037 * (0.019) (0.011) -0.010	0.042 * * (0.019) (0.010) -0.008	0.010 (0.024) (0.010) -0.005	0.044 * * (0.022) (0.010) 0.001	0.034 * (0.020) (0.012) -0.016	0.022 (0.018) (0.008) -0.002		0.014 * * (0.006) (0.004) 0.001	-0.001 (0.001) (0.001) -0.000	-0.003 (0.003) (0.001) 0.001	0.031 (0.026) (0.017) -0.019	-0.006 (0.014) (0.014) -0.023 *	0.008 (0.011) (0.006) 0.000		-0.038 * * (0.018) (0.011) -0.020 *	0.019 (0.023) (0.014) -0.036 * * *	-0.021 (0.013) (0.008) -0.004	-0.002 (0.004) (0.003) -0.005 *	-0.000 (0.004) (0.003) -0.003		0.040 (0.062) (0.037) 0.060	-0.245 * (0.130) (0.070) -0.046	3064 3064
	(1) (2)	All Women	Urban Dest. Rural Dest. Urban Dest. Rural Dest.	-0.010 (0.005) (0.007) -0.017 * * *	-0.001 (0.001) (0.001) 0.001 (0.001) -0.002 * (0.001) 0.000	0.000 (0.000) (0.000) -0.000 (0.000) 0.000 (0.000) -0.000	0.007 (0.008) (0.012) 0.020 * * (0.005) -0.005 (0.008) 0.012 * *	0.000 (0.006) (0.009) 0.012 * (0.004) 0.004 (0.006) 0.006	-0.063 * * * (0.015) (0.014) -0.023 (0.011) -0.064 * * * (0.010) -0.019 *	-0.026 * * * (0.012) (0.013) 0.057 * * * (0.008) -0.026 * * (0.010) 0.047 * * *	-0.017 (0.022) (0.023) 0.027 (0.015) -0.010 (0.020) 0.021	0.016 * (0.010) (0.012) -0.015 (0.007) 0.024 * (0.009) -0.008	-0.005 (0.008) (0.011) -0.004 (0.005) 0.005 (0.008) -0.000	0.023 * (0.020) (0.015) -0.022 (0.010) 0.054 * * * (0.012) 0.006	-0.001 (0.009) (0.013) 0.005 (0.006) 0.012 (0.010) 0.008	-0.014 (0.024) (0.017) 0.018 (0.011) -0.028 (0.013) 0.002	0.039 * * * (0.024) (0.019) 0.063 * * * (0.011) 0.019 (0.012) 0.031 * * *	0.043 * * * (0.024) (0.019) 0.044 * (0.011) 0.013 (0.012) 0.030 * * *	0.030 * * * (0.009) (0.011) -0.019 * * (0.006) 0.020 * (0.009) -0.011 *	0.042 * * * (0.017) (0.013) -0.043 * * * (0.008) 0.040 * * * (0.010) -0.008	-0.001 (0.008) (0.015) -0.000 (0.005) -0.007 (0.010) -0.004	0.033 * * (0.021) (0.022) -0.048 * * (0.011) 0.024 (0.015) -0.024 * *	0.033 * * (0.017) (0.023) -0.019 (0.009) 0.017 (0.014) -0.010	0.009 (0.011) (0.024) 0.009 (0.007) 0.010 (0.017) 0.005	0.043 * * * (0.018) (0.023) 0.009 (0.010) 0.038 * (0.016) 0.003	0.030 * * (0.010) (0.019) -0.002 (0.007) 0.032 * (0.013) -0.004	0.038 * * * (0.010) (0.019) 0.005 (0.007) 0.051 * * * (0.013) 0.004		0.012 * * * (0.004) (0.005) -0.002 (0.003) 0.010 * (0.004) -0.000	-0.001 (0.001) (0.001) -0.001 (0.000) -0.001 (0.001) -0.001	-0.003 * (0.002) (0.002) 0.003 * (0.001) -0.003 (0.002) 0.002 *	0.029 * (0.020) (0.023) -0.019 (0.013) 0.026 (0.017) -0.018	0.002 (0.008) (0.011) 0.006 (0.006) 0.008 (0.009) -0.003	0.016 * * (0.008) (0.009) -0.013 (0.005) 0.020 * * (0.007) -0.007		-0.046 * * * (0.014) (0.015) -0.066 * * * (0.009) -0.055 * * * (0.012) -0.045 * * *	-0.008 (0.017) (0.020) -0.091 * * * -0.024 (0.011) (0.015) -0.070 * * *	0.001 (0.010) -0.007 (0.011) 0.018 (0.006) -0.007 (0.009)	-0.001 (0.003) -0.002 (0.003) -0.000 (0.002) -0.002 (0.002)	-0.002 (0.003) -0.004 (0.003) -0.003 (0.002) -0.003 (0.003)		0.077 * (0.044) 0.141 * * * (0.054) 0.107 * * (0.029) 0.112 * * * (0.041)	-0.189 * * (0.076) -0.064 (0.106) -0.154 (0.053) -0.054 (0.083)	6906 3842 3842 6906	p < 0.05, * * * p < 0.01
			Individual Characteristics	Male	Age in years	Age squared	Fostered	First-born	Born in Dakar	Born in rural area	Born in other country	Serere	Poular	Diola	Other ethnic group	Spouse/Parent of the Head	Child/Sibling of the Head	Other/Non-Relatives	Primary Education	Secondary Education or University	Quranic Education	Independent/Employer	Salaried Worker/Intern/Trainee	Family Worker	Student	Inactive/Unemployed	Missing Employment category	Household Characteristics	Consumption Index (adult eq.)	Household Size	Household Cell Size	Cell/Household Expenditure	Self-Reported Richer than Community	Self-Reported Poorer than Community	Community Characteristics	Other cities	Rural	Public Hospital	Nb Public Primary Schools	Nb Public Secondary Schools	County (Département) Characteristics †	Headcount Poverty	Gini Index	Observations	Standard errors in parentheses, * p < 0.10, * *	Reference for categorical variables:

Table 4 :

 4 Descriptive statistics: comparison between non-migrants and migrants All means are calculated at the individual level, to make the comparison between the different groups easier as households may include both migrants and non-migrants. Large households thus tend to be over-represented in the reporting of descriptive statistics for household variables.

	UNDP. 2009. Overcoming Barriers: Human Mobility and Development. Palgrave Macmil-
	lan.
	Zhao, Qinghua and Peter Lanjouw. 2009. "Using PovMap2-A User's Guide." The World
	Bank .

Table 5 :

 5 Urban/Rural Internal Migrations

		Urban Origin		Rural Origin			Total
	Destination	No.	%Col %Row	No.	%Col %Row	No.	%Col %Row
	Urban	284	77%	61%	184	61%	39%	468	70%	100%
	Intra-Dakar (Regional)	116	41%
	Rural	86	23%	43%	116	39%	57%	202	30%	100%
	Total	370	100%	55%	300	100%	45%	670	100%	100%
		Source: Poverty and Family Structure Survey, 2006-2007 and 2010-2012

Table 6 :

 6 Probit models of internal migration decision (marginal effects) -alternative definition of internal migrant (>10 km)

				(0.002)	(0.000)	(0.013)	(0.010)	(0.015)	(0.012)	(0.021)	(0.016)		(0.018)	(0.019)	(0.014)	(0.015)	(0.015)	(0.019)	(0.018)	(0.022)	(0.022)	(0.020)	(0.017)		(0.006)	(0.001)	(0.003)	(0.028)	(0.016)	(0.012)		(0.018)	(0.023)	(0.014)	(0.004)	(0.005)		(0.064)	(0.126)
	Men	(6)		(0.002) 0.000	(0.000) -0.000	(0.014) 0.013	(0.010) -0.003	(0.015) 0.005	(0.012) -0.008	(0.021) 0.016	(0.015) -0.005		(0.018) 0.049 * * *	(0.019) 0.100 * * *	(0.014) 0.023	(0.015) 0.036 * *	(0.015) -0.008	(0.019) 0.022	(0.018) 0.024	(0.022) 0.009	(0.022) 0.046 * *	(0.019) 0.020	(0.017) 0.021		(0.006) 0.015 * *	(0.001) -0.000	(0.003) -0.003	(0.028) 0.047 *	-0.023	0.012		(0.013) 0.025	(0.015) 0.063 * * *	-0.017	-0.004	-0.002		0.033	-0.141	3043
		(5)		(0.002) 0.000	(0.000) -0.000	(0.013) 0.014	(0.010) -0.002	(0.014) 0.007	(0.012) -0.010	(0.019) 0.010	(0.014) -0.007	(0.020)	(0.022) 0.050 * * *	(0.022) 0.098 * * *	(0.012) 0.020	(0.015) 0.035 * *	(0.014) -0.006	(0.023) 0.023	(0.023) 0.024	(0.021) 0.010	(0.025) 0.046 * *	(0.017) 0.015	(0.018) 0.023		(0.006) 0.014 * *	(0.001) -0.000	(0.003) -0.003	(0.027) 0.043	(0.013)	(0.011)		(0.016) 0.043 * * *	(0.021) 0.093 * * *	(0.013)	(0.004)	(0.004)		(0.060)	(0.113)	3043
	Women	(4)		(0.002) -0.002	(0.000) 0.000	(0.013) 0.014	(0.010) 0.012	(0.014) 0.023	(0.011) 0.001	(0.019) 0.057 * * *	(0.014) 0.019	(0.020) -0.030	(0.022) 0.037 *	(0.022) 0.027	(0.012) -0.014	(0.015) 0.003	(0.014) 0.003	(0.023) -0.015	(0.023) 0.007	(0.021) 0.024	(0.025) 0.031	(0.017) 0.020	(0.018) 0.044 * *		(0.006) 0.004	(0.001) -0.001	(0.003) -0.002	(0.027) 0.023	0.013	0.018		(0.012) -0.034 * *	(0.013) -0.027	0.006	-0.000	-0.002		0.190 * * *	-0.072	3842
		(3)	(0.008)	(0.001) -0.002	(0.000) 0.000	(0.009) 0.016	(0.007) 0.013	(0.010) 0.026 *	(0.008) 0.007	(0.014) 0.054 * * *	(0.010) 0.023 *	(0.014) -0.028	(0.013) 0.038 *	(0.014) 0.027	(0.009) -0.012	(0.011) 0.002	(0.010) 0.003	(0.015) -0.021	(0.014) -0.001	(0.015) 0.025	(0.017) 0.027	(0.012) 0.011	(0.012) 0.038 * *		(0.005) 0.001	(0.001) -0.001	(0.002) -0.003	(0.019) 0.024	(0.010)	(0.008)		(0.012) 0.001	(0.015) 0.016	(0.010)	(0.003)	(0.003)		(0.044)	(0.084)	3842
	All	(2)	(0.008) -0.016 * *	(0.001) -0.001	(0.000) -0.000	(0.009) 0.016 *	(0.007) 0.006	(0.010) 0.016	(0.008) -0.003	(0.014) 0.038 * * *	(0.010) 0.008	(0.014) -0.017	(0.013) 0.045 * * *	(0.014) 0.059 * * *	(0.009) 0.002	(0.011) 0.017	(0.010) -0.003	(0.015) 0.008	(0.014) 0.017	(0.015) 0.017	(0.016) 0.040 * *	(0.012) 0.018	(0.012) 0.034 * * *		0.009 * (0.004)	-0.001 (0.001)	-0.003 (0.002)	0.036 * (0.019)	-0.001	0.015 *		-0.008 (0.009)	0.009 (0.010)	-0.005	-0.002	-0.002		0.124 * * *	-0.090	6906	p < 0.01
		(1)	-0.016 * *	-0.001	0.000	0.016 *	0.006	0.017 *	-0.002	0.034 * *	0.010	-0.015	0.045 * * *	0.059 * * *	0.002	0.017	-0.002	0.004	0.014	0.019	0.039 * *	0.013	0.033 * * *		0.007	-0.001	-0.003	0.033 *				0.021 * *	0.048 * * *							6906	p < 0.05, * * *
		Individual Characteristics	Male	Age in years	Age squared	Fostered	First-born	Serere	Poular	Diola	Other Ethnic Group	Spouse/Parent of the Head	Child/Sibling of the Head	Other/Non-Relatives	Primary Education	Secondary Education or University	Quranic Education	Independent/Employer	Salaried Worker/Intern/Trainee	Family Worker	Student	Inactive/Unemployed	Missing Employment Category	Household Characteristics	Consumption Index (adult eq.)	Household Size	Household Cell Size	Cell/Household Expenditure	Self-Reported Richer than Community	Self-Reported Poorer than Community	Community Characteristics	Other cities	Rural	Public Hospital	Nb Public Primary Schools	Nb Public Secondary Schools	County (Département) Characteristics †	Headcount Poverty	Gini Index	Observations	Standard errors in parentheses, * p < 0.10, * *

α Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † Department Characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey

Table 9 :

 9 Multinomial Logit models of rural/urban migration decision (marginal effects) -intra-Dakar movers treated as non-migrants

	(1) (2) (3)	All Urban Origin Rural Origin	Urban Dest. Rural Dest. Urban Dest. Rural Dest. Urban Dest. Rural Dest.	Individual Characteristics	(0.009) Male -0.006 (0.006) -0.016 * * * (0.005) -0.014 * (0.007) -0.008 (0.005) 0.001 (0.010) -0.034 * * *	(0.001) Age in years -0.001 (0.001) 0.000 (0.001) -0.000 (0.001) 0.002 (0.001) -0.002 (0.002) -0.001	(0.000) Age squared 0.000 (0.000) -0.000 (0.000) 0.000 (0.000) -0.000 * (0.000) 0.000 (0.000) -0.000	(0.011) Fostered 0.004 (0.008) 0.012 * * (0.005) -0.002 (0.009) 0.011 * * (0.005) 0.012 (0.013) 0.013	(0.008) First-born -0.003 (0.006) 0.005 (0.004) -0.000 (0.007) -0.004 (0.005) -0.006 (0.010) 0.016 * *	(0.037) Born in Dakar -0.049 * * * (0.011) -0.018 * (0.011) -0.047 * * * (0.011) -0.010 (0.008) -0.010 (0.029) 0.026	(0.026) Born in rural area -0.019 * * (0.009) 0.048 * * * (0.008) -0.009 (0.008) 0.037 * * * (0.007) -0.038 * (0.020) 0.017	(0.037) Born in other country -0.004 (0.017) 0.023 (0.015) -0.023 (0.023) 0.015 (0.014) 0.021 (0.030) -0.007	(0.012) Serere 0.013 (0.008) -0.010 (0.007) 0.006 (0.011) -0.017 * (0.010) 0.004 (0.012) -0.007	(0.010) Poular -0.011 (0.007) -0.001 (0.005) 0.007 (0.008) 0.008 (0.005) -0.048 * * * (0.014) -0.012	(0.024) Diola 0.007 (0.011) 0.003 (0.010) 0.014 (0.012) -0.002 (0.009) -0.014 (0.023) 0.022	(0.011) Other ethnic group 0.000 (0.008) 0.008 (0.006) -0.009 (0.011) -0.002 (0.007) -0.008 (0.014) 0.015	(0.019) Spouse/Parent of the Head -0.014 (0.012) 0.008 (0.011) -0.008 (0.014) 0.014 (0.015) -0.013 (0.022) -0.013	(0.019) Child/Sibling of the Head 0.030 * * * (0.011) 0.037 * * * (0.011) 0.015 (0.012) 0.042 * * * (0.015) 0.055 * * * (0.020) 0.025	(0.019) Other/Non-Relatives 0.033 * * * (0.011) 0.036 * * * (0.011) 0.037 * * * (0.012) 0.047 * * * (0.014) 0.035 * (0.021) 0.007	(0.012) Primary Education 0.023 * * * (0.007) -0.011 * (0.006) 0.008 (0.009) -0.010 * (0.006) 0.036 * * * (0.012) -0.010	(0.015) Secondary Education or University 0.033 * * * (0.009) -0.007 (0.008) 0.030 * * * (0.009) -0.013 * (0.007) 0.026 (0.016) 0.014	(0.009) Quranic Education 0.001 (0.009) -0.004 (0.005) 0.001 (0.012) -0.004 (0.006) -0.005 (0.013) -0.004	(0.037) Independent/Employer 0.022 * (0.013) -0.025 * * (0.011) 0.012 (0.020) -0.011 (0.015) 0.014 (0.022) -0.061 *	(0.023) Salaried Worker/Intern/Trainee 0.022 * (0.012) -0.011 (0.009) 0.004 (0.019) -0.006 (0.014) 0.025 (0.021) -0.010	(0.011) Family Worker 0.014 (0.013) 0.005 (0.007) -0.002 (0.033) 0.016 (0.017) 0.026 (0.017) 0.009	(0.019) Student 0.036 * * * (0.013) 0.003 (0.010) 0.011 (0.021) 0.011 (0.015) 0.065 * * * (0.020) -0.008	(0.011) Inactive/Unemployed 0.019 * (0.011) -0.003 (0.007) -0.002 (0.019) -0.005 (0.014) 0.035 * * (0.015) 0.009	(0.011) Missing employment category 0.033 * * * (0.011) 0.005 (0.007) 0.025 (0.019) 0.012 (0.013) 0.026 * (0.015) -0.004	Household Characteristics	(0.006) Consumption Index (adult eq.) 0.007 * * (0.004) -0.001 (0.003) 0.005 (0.004) 0.000 (0.003) 0.008 (0.007) -0.002	(0.001) Household Size -0.000 (0.001) -0.001 (0.000) -0.001 (0.001) -0.001 (0.001) -0.000 (0.001) -0.001	(0.002) Household Cell Size -0.003 * (0.002) 0.002 * (0.001) -0.003 (0.002) 0.001 (0.001) -0.004 (0.003) 0.004 *	(0.026) Cell/Household Expenditure 0.043 * * * (0.015) -0.017 (0.013) 0.025 (0.018) -0.017 (0.013) 0.068 * * (0.027) -0.029	(0.014) Self-Reported Richer than Community -0.006 (0.008) -0.003 (0.006) -0.006 (0.010) 0.008 (0.006) -0.017 (0.014) -0.020	(0.010) Self-Reported Poorer than Community 0.008 (0.006) -0.007 (0.005) 0.015 * * (0.007) 0.004 (0.005) -0.006 (0.012) -0.018 *	Community Characteristics	Other cities 0.039 * * * (0.012) -0.045 * * * (0.009) 0.023 * * (0.011) -0.024 * * * (0.007)	Rural 0.076 * * * (0.015) -0.069 * * * (0.011)	(0.020) Public Hospital -0.006 (0.008) -0.007 (0.006) 0.004 (0.008) -0.007 (0.006) -0.077 * * (0.030) -0.006	(0.004) Nb Public Primary Schools -0.000 (0.002) -0.003 (0.002) 0.002 (0.003) -0.002 (0.002) -0.002 (0.004) -0.003	(0.006) Nb Public Secondary Schools 0.002 (0.002) -0.003 (0.002) -0.001 (0.003) 0.000 (0.002) 0.003 (0.005) -0.018 * * *	County (Département) Characteristics †	(0.071) Headcount Poverty -0.030 (0.036) 0.116 * * * (0.029) 0.036 (0.043) 0.052 * (0.031) -0.150 * * (0.067) 0.219 * * *	(0.089) Gini Index -0.038 (0.064) -0.058 (0.052) 0.012 (0.101) -0.009 (0.087) 0.084 (0.106) -0.076	Observations 6915 6915 3985 3985 2930 2930	Standard errors in parentheses, * p < 0.10, * * p < 0.05, * * * p < 0.01	Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar	† County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009)	Source: Poverty and Family Structure Survey, 2006-2007 and 2010-2012

Table 10 :

 10 Descriptive statistics: comparison between internal migrants (distance > 5km), deceased, international migrants, movers

	(9)	t/χ 2
	(8)	t/χ 2
	(7)	t/χ 2
	(6)	t/χ 2
	(1) (2) (3) (4) (5)	Migrant Deceased Abroad Moved Lost
	(distance < 5km) and attritors

Table 11 :

 11 Descriptive statistics: comparison between internal migrants (distance > 5km), deceased, international migrants, movers (distance < 5km) and attritors (continued)

Table 12 :

 12 Probit models of internal migration decision including attrition (marginal effects)

						(0.002)	(0.000)	(0.016)	(0.012)	(0.019)	(0.014)	(0.029)	(0.017)	(0.062)	(0.019)	(0.021)	(0.017)	(0.017)	(0.017)	(0.022)	(0.022)	(0.031)	(0.029)	(0.023)	(0.022)		(0.008)	(0.001)	(0.003)	(0.031)	(0.016)	(0.014)		(0.019)	(0.027)	(0.016)	(0.004)	(0.005)		(0.074)	(0.156)
	Probits on Migration -Attritors treated as Migrants Probits on Attrition	All Women Men All Women Men	(1) (2) (3) (4) (5) (6)	Individual Characteristics	Male 0.013 (0.011) 0.037 * * * (0.009)	Age in years -0.005 * * * (0.002) -0.008 * * * (0.002) 0.001 (0.003) -0.004 * * * (0.001) -0.006 * * * (0.002) 0.000	Age squared 0.000 (0.000) 0.000 * * * (0.000) -0.000 (0.000) 0.000 (0.000) 0.000 * * * (0.000) -0.000	Fostered 0.029 * * (0.013) 0.034 * * (0.017) 0.019 (0.019) 0.012 (0.010) 0.021 (0.013) -0.002	First-born -0.009 (0.010) 0.004 (0.013) -0.026 * (0.014) -0.017 * * (0.008) -0.010 (0.010) -0.025 * *	Serere 0.062 * * * (0.014) 0.089 * * * (0.019) 0.027 (0.022) 0.050 * * * (0.011) 0.079 * * * (0.014) 0.006	Poular 0.022 * (0.011) 0.036 * * (0.015) 0.005 (0.017) 0.029 * * * (0.009) 0.040 * * * (0.012) 0.012	Diola 0.026 (0.021) 0.061 * * (0.028) -0.022 (0.033) -0.014 (0.018) -0.001 (0.023) -0.041	Other Ethnic Group 0.063 * * * (0.014) 0.072 * * * (0.019) 0.048 * * (0.021) 0.052 * * * (0.011) 0.054 * * * (0.015) 0.047 * * *	Spouse/Parent of the Head -0.008 (0.017) 0.003 (0.026) 0.173 * * (0.080) 0.014 (0.014) 0.030 (0.020) 0.169 * * *	Child/Sibling of the Head 0.036 * * (0.017) 0.058 * * (0.029) 0.016 (0.023) -0.002 (0.014) 0.017 (0.022) -0.024	Other/Non-Relatives 0.101 * * * (0.017) 0.082 * * * (0.028) 0.133 * * * (0.025) 0.056 * * * (0.014) 0.058 * * * (0.022) 0.055 * * *	Primary Education -0.052 * * * (0.013) -0.050 * * * (0.017) -0.058 * * * (0.020) -0.069 * * * (0.011) -0.050 * * * (0.013) -0.098 * * *	Secondary Education or University -0.008 (0.014) -0.009 (0.020) -0.013 (0.021) -0.036 * * * (0.011) -0.022 (0.015) -0.058 * * *	Quranic Education -0.027 * * (0.014) -0.004 (0.019) -0.061 * * * (0.020) -0.033 * * * (0.011) -0.012 (0.015) -0.063 * * *	Independent/Employer 0.012 (0.020) -0.016 (0.030) 0.035 (0.026) -0.002 (0.016) -0.003 (0.025) 0.004	Salaried Worker/Intern/Trainee 0.025 (0.020) 0.063 * * (0.031) 0.007 (0.026) 0.007 (0.016) 0.063 * * (0.025) -0.022	Family Worker 0.007 (0.023) 0.027 (0.031) -0.010 (0.034) -0.024 (0.021) -0.015 (0.029) -0.018	Student 0.037 (0.024) 0.023 (0.036) 0.061 * (0.033) 0.000 (0.020) 0.003 (0.030) 0.019	Inactive/Unemployed 0.012 (0.018) 0.023 (0.025) 0.023 (0.028) -0.006 (0.015) 0.007 (0.021) 0.007	Missing Employment Category 0.043 * * (0.018) 0.061 * * (0.026) 0.025 (0.025) 0.010 (0.015) 0.023 (0.022) 0.003	Household Characteristics	Consumption Index (adult eq.) 0.040 * * * (0.006) 0.040 * * * (0.009) 0.040 * * * (0.009) 0.030 * * * (0.005) 0.032 * * * (0.007) 0.026 * * *	Household Size -0.002 * (0.001) -0.002 (0.001) -0.002 (0.002) -0.001 (0.001) -0.001 (0.001) -0.001	Household Cell Size -0.015 * * * (0.003) -0.009 * * (0.004) -0.017 * * * (0.004) -0.013 * * * (0.002) -0.009 * * * (0.003) -0.014 * * *	Cell/Household Expenditure 0.124 * * * (0.025) 0.062 * (0.036) 0.180 * * * (0.038) 0.101 * * * (0.020) 0.054 * (0.028) 0.152 * * *	Self-Reported Richer than Community 0.025 * * (0.013) 0.030 * (0.017) 0.020 (0.020) 0.029 * * * (0.010) 0.023 * (0.013) 0.036 * *	Self-Reported Poorer than Community 0.022 * * (0.011) 0.007 (0.015) 0.036 * * (0.017) 0.011 (0.009) -0.007 (0.012) 0.027 *	Community Characteristics	Other cities -0.071 * * * (0.016) -0.079 * * * (0.021) -0.058 * * (0.023) -0.031 * * (0.013) -0.022 (0.016) -0.039 * *	Rural -0.098 * * * (0.021) -0.115 * * * (0.028) -0.066 * * (0.031) -0.092 * * * (0.017) -0.086 * * * (0.022) -0.092 * * *	Public Hospital -0.024 * (0.013) -0.005 (0.017) -0.048 * * (0.019) -0.024 * * (0.010) -0.018 (0.013) -0.031 * *	Nb Public Primary Schools -0.005 (0.004) -0.006 (0.005) -0.005 (0.005) -0.002 (0.003) -0.005 (0.004) 0.001	Nb Public Secondary Schools 0.001 (0.004) 0.002 (0.005) 0.002 (0.006) 0.006 * (0.003) 0.008 * (0.004) 0.005	County (Département) Characteristics †	Headcount Poverty 0.088 (0.059) 0.156 * * (0.079) 0.035 (0.088) -0.056 (0.048) -0.039 (0.062) -0.041	Gini Index -0.063 (0.119) -0.054 (0.156) -0.105 (0.184) 0.169 * (0.099) 0.161 (0.125) 0.169	Observations 7932 4338 3594 7932 4338 3594	Standard errors in parentheses, * p < 0.10, * * p < 0.05, * * * p < 0.01	Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar	† County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009)	Source: Poverty and Family Structure Survey, 2006-2007 and 2010-2012

Table 13 :

 13 Determinants of migration distance -Heckman model estimation (sample: adult migrants (+15 years) > 5km) Reference for categorical variables: Wolof/Lebou, head of household, no education, agricultural employment, Dakar, self-reported household vs community wealth: similar † County characteristics computed based on 2002 Senegalese Census (ANSD); Headcount Poverty & Gini Index generated with PovMap2 (World Bank, 2009) Source: Poverty and Family Structure Survey

	(6)
	Men
	(5)
	(4)
	Women
	(3)
	(2)
	All
	(1)

Both measures were obtained using the PovMap2 software developed by the World Bank(Zhao and Lanjouw, 2009;[START_REF] Elbers | Micro-level estimation of poverty and inequality[END_REF]

Senegal was subdivided into 34 counties (départements) in 11 regions in 2006. In 2008, Senegal underwent administrative reforms: the country is currently subdivided into 45 counties (départements) and 14 regions.

Child fostering, in particular, is widespread in Senegal[START_REF] Beck | Child fostering in Senegal[END_REF]

Ten teams of two to three surveyors were managed on the field by one controller each, who was in particular in charge of checking compliance with procedures and of verifying that accurate tracking information had been reported by surveyors.

Additional Tables and Figures (for online publication)