Gendered Patterns of Migration in Rural South Africa

Gender is increasingly recognised as fundamental to understanding migration processes, causes, and consequences. In South Africa, it is intrinsic to the social transformations fueling high levels of internal migration and complex forms of mobility. Although female migration in Africa has often been characterised as less prevalent than male migration and primarily related to marriage, in South Africa, a feminisation of internal migration is underway, fueled by women ’ s increasing labour market participation. In this paper, we report sex differences in patterns, trends, and determinants of internal migration based on data collected in a demographic surveillance system between 2001 and 2006 in rural KwaZulu-Natal. We show that women were somewhat more likely than men to undertake any migration, but sex differences in migration trends differed by migration ﬂ ow, with women more likely to migrate into the area than men and men more likely to out-migrate. Out-migration was suppressed by marriage, particularly for women, but most women were not married; both men ’ s and women ’ s out-migrations were undertaken mainly for purposes of employment. Over half of female out-migrations (vs 35% of male out-migrations) were to nearby rural areas. The ﬁ ndings highlight the high mobility of this population and the extent to which gender is intimately related to the processes determining migration. We consider the implications of these ﬁ ndings for the measurement of migration and mobility, in particular for health and social policy and research among highly mobile populations in southern Africa. Copyright © 2013 John Wiley & Sons, Ltd.


INTRODUCTION
G ender is increasingly recognised as fundamental to understanding migration processes, causes, and consequences. The first critical analyses of migration research through the lens of gender emerged some three decades ago, directing attention to the male gender bias embedded in migration studies (Pedraza, 1991;Tienda and Booth, 1991;Bilsborrow, 1992;Chant and Radcliffe, 1992;Hugo, 1993). Women's mobility in sub-Saharan Africa has continued to receive little attention in migration studies, in part because of an enduring paucity of nationallevel data for the study of sex-specific migration patterns in the region. However, a small number of recent studies using sex-specific data on migration (Beauchemin and Bocquier, 2004;Collinson et al., 2006;Collinson, 2009;Beguy et al., 2010;Reed et al., 2010) have yielded growing evidence for a feminisation of migration in sub-Saharan Africa, as in other developing regions (Bilsborrow, 1992;Hugo, 1993;Zlotnick, 2003). In South Africa, the available data suggest that a feminisation of internal labour migration has been underway for at least three decades (Casale and Posel, 2002;Feinstein, 2005;Posel, 2006). In the 1990s, some 16% of the rural South African population migrated annually to urban areas (Anderson, 2006) to seek opportunities and provide financial support to households of origin (van der Berg et al., 2002;Posel and Casale, 2003;Collinson et al., 2006;Collinson et al., 2009).  census data showed that 42% of citizens of African origin had ever moved from one district to another and that 51% of these migrants were women (Wentzel et al., 2006). A number of studies using data from rural demographic surveillance sites (DSS) have documented an increasing trend of migration to other rural villages, semi-urban towns, and the rural perimeters of metropolitan areas. A higher proportion of female than male migrants travel to these areas, which are closer to rural and periurban homes in the Agincourt DSS population in Mpumalanga Province (Collinson et al., 2006;Collinson et al., 2007) and the DSS population for the present study in KwaZulu-Natal (KZN) (Lurie et al., 1997;Muhwava et al., 2010). 1 In Agincourt, rural-to-rural and rural-to-town migration flows have become more prominent (Collinson et al., 2006) 2 than migrations to the Johannesburg/Gauteng area. Female migration increased threefold between 1997 and 2001 (Collinson et al., 2006) and continued to increase from 1999 to 2003 (Collinson, 2007), with women aged 15-25 years being the most mobile population category. For the KZN population (this study), previous analyses also highlighted women's predominance in localised, shorter-distance migration flows (Muhwava et al., 2010).
Complex, novel migration and mobility patterns are emerging in South Africa, concurrent with rapid social transformations in gender underway in the nation. These patterns warrant closer attention to women's migration and its causes and consequences. In this paper, we present findings of a study on sex differences in the trends, patterns, and determinants of migration in a population living in a primarily rural area of KZN from 2001 to 2007. We use uniquely detailed data and a range of measures to examine the degree to which they adequately encompass both men's and women's participation in migration. Finally, we investigate possible sex differences in the determinants of migration and consider their implications for current and future studies of gender and migration in southern Africa.

Historical Context
The gendered patterns of migration in today's South Africa are rooted in its unique history as an extreme example of modern overseas settlement colonisation (Osterhammel, 1997). From the 17th century through the end of apartheid in the early 1990s, South Africa's governmental policies sought to extract the cheap labour of Black people to support the privileged position of White people (Feinstein, 2005). Male temporary labour migration was a cornerstone of South Africa's segregationist economy. 'Influx control' legislation, that is, urban residency and land ownership restrictions on the Black population, and apartheid policies governing the residence and movement of Black South Africans sought, among other things, to prevent women from migrating from rural areas (Preston-Whyte, 1978). Yet despite the state's best efforts, the male migrant labour system did not produce a stable population of women 'left behind' to maintain rural homesteads. Quite to the contrary, women have migrated independently to and within South Africa at least since the late 19th and early 20th centuries, when many moved to the Witwatersrand to pursue economic opportunities in the gold boom economy (van Onselen, 1982;Bonner, 1990). They came from rural areas of South Africa and from Swaziland and Bechuanaland (Botswana) (Cockerton, 1995;Dodson and Crush, 2004) to participate in the domestic labour and informal sectors, which evolved in tandem with the male migrant labour system (Walker, 1990). The apartheid regime's influx control laws specifically excluded women as labour immigrants to South Africa (Wilkinson, 1983), but the internal migration of women in southern African 'sending' nations of Lesotho, Swaziland, Mozambique, and Botswana increased over the 1970s: while the burden of agricultural production, falling exclusively upon women, became heavier, arable land became scarcer in sending areas, exacerbated by new systems of land tenure (Spiegel, 1981;Wilkinson, 1983). A similar phenomenon occurred in South Africa's internal migrant sending areas, leading to dramatic sex imbalances in the towns of the former 'homelands' (Preston-Whyte and Sibisi, 1975).
Since at least the 1970s, the destinations of female migrants appear to have not been the distant large cities to which men migrated, but rather the small regional towns, peri-urban or semi-rural employment zones, or the informal peripheries of cities, all of which are closer to the rural homesteads to which women remain tied. In her history of a town in North West Province, Bozzoli (1991) noted that 'Migration [of women] did not involve spending the long lonely periods away from home which the more distant migrant would experience. The surrounding towns and cities were relatively well known and understood, in ways that reflected the mental maps Bafokeng women held of their own rural universe' (p. 95). Indeed, despite their weak or declining economic bases, informal settlement areas and peripheral, regional towns in South Africa have continued to be focal points for female migrants. A case study of migration in and out of a township area in northern KZN (Todes, 1998) documented changes in community members' attitudes towards female migration as economic conditions worsened over the 1990s: confronting 'older prejudices', 'families on the whole did not seem to prevent daughters from moving, and in fact were frequently supportive of their daughters' (ibid.: 325).

The Post-apartheid Era
The political, economic, and social changes of the past two decades have significantly altered the context, drivers, and legislative controls of migration in South Africa. In 1986, apartheid influx control measures were formally abolished, 'after a period in which it had broken down as people defied laws and streamed to the cities' (Todes, 1998: 311). An assumption had been that 'artificial' towns and peripheral industrial areas, created by apartheid through forced removals and influx controls, would 'wither away' after apartheid as people continued to migrate to urban areas (ibid.; Casale and Posel, 2002). However, net rural-to-urban migration rates are estimated to have increased from 2% in 1980-1984 to 15.4% in 1995-1999 per 1,000 population in South Africa (Anderson, 2006), with the caveat that the designation of 'urban' is difficult and controversial in the southern African context (Billsborrow, 1998;Anderson, 2006;Collinson, 2007). No longer subject to brutal spatial interventions by the apartheid state, informal settlement areas 3 have dramatically grown in size in South Africa over the past two to three decades, in a process of 'displaced urbanisation' (Anderson, 2006). Concurrent with these changes, the HIV/AIDS epidemic rapidly spread between urban areas and from urban to rural areas in southern Africa, via the corridors of major population movement. The contributing role of South Africa's male migrant labour system to the nation's enormous epidemic is well documented (Jochelson et al., 1991;Abdool Karim et al., 1992;Williams and Campbell, 1996;Campbell, 2000Campbell, , 2001Hope, 2000). Perhaps as a result, the literature on migration and HIV has largely focused on risks to male labour migrants and their non-migrant female partners or migrants overall (Jochelson et al., 1991;Bwayo et al., 1994;Nunn et al., 1995;Hope, 2000;Lurie et al., 2003). Those measuring HIV risks to women via their direct involvement in migration, however, have documented high acquisition and transmission risks among female migrants (Abdool Karim et al., 1992;Pison et al., 1993;Boerma et al., 2002;Zuma et al., 2003;Lydie et al., 2004;Kishamawe et al., 2006;Camlin et al., 2010). Previous research in the population for this study found higher HIV prevalence among recent female migrants than among male migrants or non-migrants of either sex. Women's internal migration may be an under-recognised social antecedent to the HIV epidemic in South Africa (Camlin et al., 2010).

Causes of the Feminisation of Migration in South Africa
The factors driving a feminisation of internal migration in South Africa are thus multifaceted, with unique historical antecedents, but are also well explained by the new economics of labour migration (Stark, 1991;Massey et al., 1998;Massey, 2006): where urban labour markets are volatile and insecure, a geographically stretched householdone in which members live and work in multiple placesalso diversifies its risks. In South Africa, this process of risk diversification has been highly gendered, and the large social transfers enacted after the democratic elections of 1994 may have facilitated women's labour migration. The research on pensions and remittances suggests that the presence of older women in rural households, and absence of older men and husbands, has facilitated the migration of income (Ardington and Lund, 1995;Ardington et al., 2009) but also the childcare that permitted reproductive-age women to migrate for work (Hunter, 2010;Ardington et al., 2009). This finding is supported by other research from South Africa showing that a greater percentage of female labour migrants came from households with at least one woman of pension-eligible age (41% compared with 25% in households without a female pensioner) (Posel, 2001). In the first decade of the 21st century in South Africa, the sending of a female migrant has become an essential livelihood strategy particularly advantageous to the poorest households Collinson et al., 2009).
Transformations in gender norms in South Africa are also underway, relaxing 'traditional' gender-related constraints to female labour force participation and migration. Early anthropological research in the region (e.g. Meillassoux, 1960) documented the power that chiefs, fathers, and husbands held with respect to restricting women's mobility and reinforcing their roles in rural production. Women's roles in childcare and farming reduced the likelihood of migration, as did marriage. Gendered divisions of labour were upheld by social pressure, gender ideology, and women's economic dependence in rural communities (Posel and Casale, 2003). In South Africa and surrounding nations, male migrant labour systems are thought to have contributed to turbulent gender relations and disruptions of 'traditional' norms (Spiegel, 1991;Lovett, 1996;Breckenridge, 1998;Campbell, 2001;Hunter, 2007;Smith, 2007) and to the destabilisation of family structures and marriage systems (Murray, 1976(Murray, , 1980Wilkinson, 1983;Lovett, 1996). Indeed, South Africa's marriage rates are uniquely low in the region and probably declining, 4 and the structure and composition of households are changing. Reliable nationally representative estimates of nuptiality were lacking until recently, but the Demographic and Health Surveys for South Africa found that only 34% of women of reproductive age were currently married in 1998 (Department of Health, Medical Research Council, and ORC Macro, 1998), declining to 28% in 2003(Department of Health, Medical Research Council, and ORC Macro, 2003. Previous analyses of the population for this study showed that the proportion of those that never married increased continuously from 2000 to 2006, when 69% of women had never been married . At the same time, women are participating in the labour force in greater numbers than ever before: whereas the male labour force participation rate dropped from 97% in 1960 to 65% in 1996, the rate for females rose in the same period from 30% to 49% (Feinstein, 2005).
There are few data sources for the study of sexspecific migration patterns and determinants in South Africa, and women's unique patterns and motivations for migration are not well described in the demographic literature. This study exploits a rich data source to address this gap. We present a case study of sex differences in trends, patterns, and determinants of migration in a population living in a primarily rural area of KZN from 2001 to 2007. A key aim of this analysis is to explore how the sex composition of migrants in the population shifted depending upon how migration was defined. We therefore use several measures to describe detailed patterns of migration and mobility in the adult population by sex. We examine sex differences in the individual and household characteristics that shape the likelihood of migration, in the destinations chosen by migrants over the period, and in the reasons given for migration. The data available for these analyses provide a detailed description of the gendered patterns of mobility in rural South Africa and the factors driving this mobility.

Data Source
Data are from the Africa Centre Demographic Information System (ACDIS) conducted by the Africa Centre for Health and Population Studies. Since 2000, ACDIS has collected demographic, social, and behavioural data in a population of over 100,000 individuals in the Umkhanyakude District, a predominantly rural area of KZN about 2 hours north of Durban (Tanser et al., 2008) (Fig. 1.) ACDIS was designed to closely reflect the complexity of the social organisation of rural communities of KZN and the high mobility of the population (Hosegood and Timaeus, 2005a;Tanser et al., 2008). The surveillance area is 435 km 2 , and all bounded structures within the area that either have a residential purpose (homesteads) or provide a service (e.g. schools, clinics, and churches) are registered and updated routinely. The households that are resident at these structures are registered and followed, as are all members of these households.
In ACDIS, individuals are included in the surveillance population on the basis of being a member of a household in the study area irrespective of whether the person is a resident or not (Hosegood and Timaeus, 2005a;Tanser et al., 2008). The residency status (whether resident or non-resident) and place of residence are routinely recorded for all household members. The place of residence is in most cases the place where a person keeps their daily belongings and spends most nights. Although ACDIS can record an individual as being a member of more than one household at a time, 5 for instance, in the case of polygamous marriage, an individual can only be recorded as being a resident within one bounded structure at any point in time. 6 At each fieldworker visit, any change in household residency is recorded, together with information about the origin or destination and date of the move. Changes in residency are referred to as migration events. These are classified as in-migrations (a migration into a homestead within the surveillance area), internal migrations (migrations within the surveillance area), or out-migrations (migration to a homestead outside of the area). A household migration involves a change of residence by all resident members of the household to another homestead; both individual and household migrations are recorded. At each visit to a household, the household roster is reviewed and updated on the basis of any changes due to events including births, deaths, and migration. The pattern of household presence (number of nights slept in the household since the previous visit and whether present on previous night) is also recorded for each household member. This analysis used routinely collected demographic data and information from the first round of the Household Socio-economic Survey (HSE-1), collected in 2001, about the household (household HSE-1 questionnaire) and each member of the household (individual HSE-1 questionnaire).

Setting
The surveillance area encompasses both land under tribal authority (Mpukunyoni) that was designated as a Zulu 'homeland' under the former apartheid policy and a township (KwaMsane) under municipal authority (Fig. 1). Previous analyses of ACDIS data indicate that there were 85,502 individuals in the population in the midyear of 2001 (Muhwava et al., 2010). Some 28% was non-resident household members on that date (ibid.); the proportion of adult female non-residents has been lower than that of male non-residents since the start of ACDIS. Infrastructure and living conditions are poor: in 2001, 50% of households had no electricity, and only 13% had access to piped water. There is little subsistence agriculture in the area, and most households rely on pension, child support grants, and wage income (Case and Ardington, 2004;Case et al., 2005;Ardington et al., 2009). Mortality in the study area rose sharply in the late 1990s, largely as a result of HIV: by 2000, the probability of dying between the ages of 15 and 60 years was 58% for women and 75% for men; AIDS with and without tuberculosis was the leading cause of death in adulthood (48%) (Hosegood et al., 2004b). In 2006, 27% of female and 13.5% of male residents were HIV infected (Welz et al., 2007). HIV prevalence was yet higher in non-residents, at 34% among men aged 15-54 years and 41% among women aged 15-49 years (ibid.). HIV incidence was sustained at a high level over the years 2003-2007, at an overall rate of 3.4 per 100 person-years . Overall population mortality and HIV-related adult mortality declined significantly between 2002 and 2006 following the rollout of HIV antiretroviral treatment in the population .

Populations
This analysis begins with a presentation of sex differences in migration patterns and determinants for the first 2-year period from the start of ACDIS, 2001ACDIS, -2003. An analysis of sex differences in the pattern of presence in the household in the previous 4 months was carried out on the 1 January 2001 population, and age-specific rates of migration, by type of migration and sex, were also generated for this population. We also examine sex-specific trends in migration from 2001 through 2006, defining the populations for rates (i.e. the denominators) as all individuals aged 15 years and older who were members of households on 1 January of the calendar year. The numerators for rates were defined as the number of individuals who had at least one migration event, by type, within the year.
Analyses of characteristics associated with migration by sex were carried out on the 1 January 2001 population. We focus on individual, rather than household, migrations in 2001-2003, which comprised the majority of migration events over the period. We examined sex differences in migration destinations over the years 2001-2006, using the migration event as the unit of analysis (as information on destinations was often not available for out-migrants, the full 6 years of data was used to maximise non-missing responses). Table 1 Adjustment for selection bias in the first-round Household Socio-economic Survey data Of the population of 48,163 adults aged 18 years and older, HSE-1 data were available for 41,919 individuals (87%). Other ACDIS data on the characteristics of the 6,244 adults for whom HSE-1 data were not available 7 showed that they differed from the population for whom HSE-1 data were available. To adjust for this selection bias, we used a propensity score weighting approach (Little and Rubin, 2002), generating a score representing the propensity of 'participation' in HSE-1 for all of the members of the population and using this score to apply a non-response adjustment weight to the analyses. 8 The weight was used as a frequency weight for analyses shown in Tables 2 and 3. (Unweighted data are  shown in Appendix Tables A.1

Variables
To identify characteristics predictive of migration, we used data on socio-economic and other characteristics of individuals that were collected prior to their subsequent migration events. 9 That is, we examine only the migrations undertaken after the HSE-1 data were collected. For this paper, we examine residency status and individual out-migration and in-migration events as defined in ACDIS and two measures of short-term mobility: a dichotomous measure of present versus not present at household on the night prior to data collection (the first visit after 1 January 2001) and a categorical measure of the extent of recent presence in the household, with four levels (in the household every night, present most nights, present approximately half of the nights, and present few or no nights in the previous 4 months).
On the basis of prior research, we examined a set of characteristics likely to be associated with migration: sex, age, employment status, education level, marital/partnership status, and parenting status. 10 We also examine the characteristics of individuals' households including size, the sex and number of pension-eligible adults (ages 60 years and older for women and 65 years and older for men), the dependency ratio (the ratio of children aged 0-17 years and pension-eligible adults to working-age adults), and measures of household socio-economic status, including electricity, water source and sanitation, and household assets. The asset scale is a sum of the number of up to 17 assets in the household, divided into tertiles to provide lower-level, middle-level, and higherlevel groupings of economic status. A dichotomous measure of the occurrence of any death of another adult in the household in 2001-2002 prior to a migration was also included. The comparison category for this variable included individuals for whom no adult in the household died in the 2-year period prior to migration and individuals who may have lost another adult household member to death after migration. This variable was included because previous research in the population showed that households experiencing more than one adult death or an injury death were more likely than other households to dissolve within 2 years of the death (Hosegood et al., 2004a). Table 3 shows the distribution of individual outmigrations by sex and type of destination; the categories of destinations included rural versus urban, and within the urban category, whether formal or informal. Destinations were also classified into the categories 'Mpukunyoni tribal area of Hlabisa district', which refers to areas that are within the local tribal area but not part of the ACDIS surveillance; 'elsewhere in KZN', referring to withinprovince migrations beyond Mpukunyoni and Hlabisa; and 'other South African province or international'. The latter category combines migrations to other South African provinces with migrations to other African countries and beyond, as international migrations were few in number (<1% of adult out-migrations in 2001-2006.)

Statistical analysis
Multiple logistic and ordinal logit regression models were fitted to characterise sex differences in patterns and determinants of migration events. For the basic logit model, the logistic transformation of the success probability p is given by where b denotes the (K + 1) Â 1 vector of regression coefficients to be estimated (Powers and Xie, 2000). Given that we use several household-level variables in these models, we adjusted standard errors for the clustering of individuals within households.
We calculated age-adjusted sex differences in the predicted probability of degree of presence in the household by fitting an ordinal logit regression model with age and sex as independent variables and a four-level dependent variable measuring household presence. The cumulative probability of the ordered logit model, a 'proportional odds model', is written as

Sex Differences in Migration and Mobility Across Several Measures
As shown in Table 1, whether men or women predominated within the category of 'migrant' varied by the definition and measure used. In a composite measure of individual migration of any type, women slightly predominated: 19.4% of all adult women versus 19.1% of adult men, overall, migrated within a 2-year period. Yet men (50.4%) were more likely than women (38.5%) to be a non-resident household member; and male residents were more likely than female residents to have out-migrated at least once within 2 years (15.8% vs 10.6%). Men were also less likely than women to have been present in the household on the night of the first visit after 1 January 2001. The level of recent mobility in the population was quite high, even among residents, who may be presumed to be more residentially stable than non-resident household members. Resident women had only a slightly higher probability than resident men (0.50 vs 0.47) of having been present every night in the household and a slightly lower probability than men (0.41 vs 0.43) of having been present most nights in the previous 4 months (Fig. 2). Among non-residents, men were more likely than women (0.49 vs 0.40) to have been in the home few or no nights, whereas women had higher probabilities than men of being in the home approximately half of the nights (0.28 vs 0.26), most nights (0.19 vs 0.15), and every night (0.14 vs 0.10) in the previous 4 months. Thus, although women are more likely to be classified as resident, they are nonetheless highly mobile: only half of resident women were present in the household every night in the past 4 months, and some 10% were present approximately half or fewer nights. Moreover, those classified as non-resident were often present in the household, with women more likely than men to have been present at least some nights.

Sex and Age Patterns of Migration Rates in 2001, by Type of Migration
Sex differences in migration rates were larger in some age groupings than in others, as shown in Figures 3 and 4. In 2001, in-migration rates for both non-resident men and women peaked in the 20-24-year age group, but the rates diverged widely by sex: 108 female versus 86 male nonresidents in this group (per 1,000) in-migrated in 2001 (Fig. 3). In-migration rates declined in the age 30 years and older groups and rose again in the 40 years and older groups, but rates were higher for women than for men across all ages. The widest interval of sex difference was seen in the 30-34-year age group, in which 68 female versus 45 male per 1,000 non-residents in-migrated. An opposite pattern was seen in the age-specific out-migration rates of resident men and women in 2001 (Fig. 4): out-migration rates of men exceeded those of women in every age group except the 15-19-year group, in which 61 women versus 55 men per 1,000 out-migrated; and outmigration rates were virtually the same among men and women aged 25-29 years. The highest rate was again in the 20-24-year age group. Rates of in-migration remained higher for women than for men (although the gap narrowed somewhat in [2005][2006], averaging 81 per 1,000 for female and 70 per 1,000 for male non-residents over the 6-year period. Individual out-migration rates remained higher among male than among female residents, averaging 99 for men and 64 for women per 1,000 over the period. Overall, the sex-specific annual rates of in-migration did not change remarkably over the period, but rates of male outmigration declined, confirming a widening sex ratio imbalance within the ACDIS population over the years (Muhwava et al., 2010.

Socio-economic and Demographic Factors Predictive of Migration
As shown in Table 2    by the type of migration. Although out-migration was negatively associated with age for both men and women, other factors were more strongly predictive of women's out-migration. Women with a marital partner had almost 60% lower odds of out-migration relative to unmarried women [adjusted odds ratio (aOR) = 0.42, vs the equivalent aOR = 0.66 in men]. The outmigration of women, only, was positively associated with having attained the highest level of secondary education or higher (aOR = 1.25; relative to those with the least education) and with the recent death of another adult in the household (aOR = 1.56) and negatively associated with sharing the same household as one's child (aOR = 0.59). The household dependency ratio also negatively influenced women's out-migration only: each unit increase in the ratio (reflecting an increase in the number of dependents relative to the number of working-age adults) reduced the odds of out-migration by 9% (aOR = 0.91). However, the number of other adults with employment in the household had no influence on out-migration, suggesting that as the ratio of dependents to working adults increased, women's out-migration is reduced more because of their involvement in caregiving than because of the suppressing effect of earned income to the household from other adults. The right columns of Table 2 show factors predictive of in-migration in the non-resident populations of female and male adults. Household members who were non-resident on 1 January 2001 but subsequently in-migrated are a special category of 'in-migrants': these are individuals who already had a significant tie to the area and are not newcomers (for whom ACDIS has no information). Many of the factors that appeared to facilitate out-migration may also constrain in-migration but, in contrast to the out-migration models, were more strongly predictive in men. In-migration was negatively associated with being employed for women (aOR = 0.72), but especially men (aOR = 0.54). In men only, in-migration was negatively associated with having attained the highest education level (aOR = 0.75) and positively associated with sharing a household with one's children (aOR = 1.30). The increasing role of men in caregiving, in the context of high HIV mortality in women, may account in part for this finding: the death of another adult predicted the in-migration of women (OR = 1.57), but especially men (OR = 1.71). Household infrastructure also appeared to facilitate men's migration: household electricity access was significantly associated with the in-migration of men only (aOR = 1.21).

Sex Differences in Out-migration Destinations
Out-migrations to rural areas were significantly more likely to be undertaken by women than men (50.4% vs 35.3%) in [2001][2002][2003][2004][2005][2006]. The outmigrations to urban areas (64.8% by men and 49.6% by women) were predominantly to formal areas for both sexes, although migrations to informal urban areas trended towards a greater proportion of women. Out-migrations to local areas near the surveillance area were more likely to be undertaken by women (29.1%) than by men (18.2%), whereas male migrations outnumbered female migrations as a proportion of international out-migration events over the period (18.0% vs 8.1%). Across many measures, women were seen to undertake more local, shorter-term migration than men and to predominate in the rural-rural migration flow.

DISCUSSION
This study documents extraordinarily high levels of mobility in a population of adults living in an area on the northern coast of KZN, South Africa; an area that in many ways is typical of the rapidly changing, and urbanising, formerly rural 'homelands' of the nation. A large proportion of members of households are living away from their homes while continuing to be socially connected to them; and despite popular assumptions that women in rural areas are the 'stay-at-home' partners of male migrants, they are far from residentially stable. Resident members of households, who were disproportionately female and may have been assumed to represent the 'stable' population, were also highly mobile. At least half of both male and female residents were absent from home at least some of the time in the previous 4 months, and only 60-70% would have been found at home on the night prior to the surveillance visit.
This study used detailed measures of migration, examining sex-specific patterns of mobility over national and provincial boundaries and shorter-distance migrations in and out of a local surveillance area and finding distinct sex differences in the patterns and determinants of migration. Men's and women's migration flows and destinations differed significantly, with overall higher rates out of, but not into, the surveillance area in men than in women in [2001][2002][2003][2004][2005][2006]. Women predominated in migration flows to other rural areas, and men in flows to urban areas; and men migrated over longer distances, greatly outnumbering women in inter-provincial and international migration. Yet when out-migration, in-migration, and localised internal migration were combined in a single indicator representing 'any migration', women's levels of participation in migration were similar or slightly higher than those of men.
The results highlight the importance of measurement both for ascertaining sex differences in migration patterns and flows and for the development of measures that accurately capture both men's and women's overall levels of participation in migration. This study exploited the unique advantages in DSS data for these purposes, providing the needed detail not available in either censuses or many existing surveys for the study of sex-specific forms of internal migration. These findings provide a quantitative referent to the historical and ethnographic accounts (e.g. Bozzoli, 1991;Todes, 1998;Hunter, 2007) of women's high levels of mobility in South Africa and of their participation in localised, rural-to-rural, and rural-to-peri-urban migration flows. They imply that health and social policy that assumes a uniform participation by women and men in processes of urbanisation, assuming equal participation by both sexes in rural-to-urban migration flows and the primacy of large urban areas as migration destinations, will under-recognise women's participation in and unique patterns of mobility. A closer attention to women's mobility reveals a rural South Africa in dramatic flux, with new configurations of household composition emerging in response to both the catastrophe of AIDS and the opportunities afforded by large social transfers (i.e. the old-age pension) and changing gender norms surrounding migration.
Mobility in the ACDIS population appears very high, compared with other South African populations: the detailed measures of migration used in ACDIS show very high rates of migration relative to national-level estimates of rural-tourban migration rates using South Africa census data (e.g. 15.6 per 1,000 in 1990-1999) (Anderson, 2006). Our findings were more comparable with those of other DSSs using 'event-based' measures of migration (Adazu, 2009) than with censusbased measures; however, ACDIS rates were higher even relative to the high in-migration and out-migration rates in the Agincourt DSS over the years 2000-2004, in which, for example, inmigration peaked at 34 and out-migration peaked at 49 per 1,000 women aged 20-24 years (Collinson et al., 2006). Although not directly comparable, the ACDIS migration rates are closer to the high rates of migration observed in DSS populations in Kenya (Collinson, 2009). For example, at the rural Kisumu site in 2002, out-migration rates were highest in women aged 20-24 years, at over 30 per 100 person-years (ibid.); female migration in Kisumu, it was noted, was not only for purposes of employment but also for marriage, which, in contrast to South Africa, is very common. Crossnational research would be needed to ascertain the reasons for similarities and differences in rates across sites in the region. However, it is equally important to study location-specific forms of mobility and the economic and social processes producing these sometimes unique, complex forms (Deane et al., 2010) and to draw inferences from these observations for similar locations.
This study also confirms prior research emphasising the saliency of women's increasing labour force participation as a driver of female migration in South Africa, as migration for nuptiality has declined (Casale and Posel, 2002) and as female migrant remittances have become a crucial livelihood strategy for the poorest households (Collinson et al., 2009). In the ACDIS population, marriage reduced the likelihood of women's migration and had no influence on men's migration, but it was uncommon: in 2001, only 20.4% of adults were currently married, although almost all were parents. Given the low rates of marriage in this population, female migrants are not predominantly young, unmarried women without children, as is the case in settings in which marriage is universal. Indeed, the findings support the proposition (Hunter, 2007) that gender norms related to migration for marriage may be changing in South Africa, as marriage remains a valued ideal that is increasingly hard to attain.
In the ACDIS population, being unemployed was associated with both men's and women's migration from the area, whereas being employed outside of the area reduced the likelihood of a return. Migrants overall were more highly educated than non-migrants; however, educational attainment was also positively associated with women's out-migration and negatively associated with men's in-migration. Further research would be needed to ascertain whether women's aspirations, tied to educational attainment, more frequently drive their migration because of the lower benefits of education for women's employment in rural places of origin or whether women experience lower returns on education in labour markets in urban destinations, facilitating their return migrations to rural areas.
A previous analysis of ACDIS data on the effects of the old-age pension on households found that the arrival of a pension facilitated the labour migration of prime-aged household members (Ardington et al., 2009). This impact was attributed both to an increase in household resources, used to stake migrants until they become self-sufficient, and to the presence of pensioners who can care for children. In this study, the presence of pension-eligible adults in the household was not significantly associated with subsequent migration. However, this study was not designed to detect whether losses or gains of pensioners in households impacted upon migration, and such an approach may be required to replicate prior results.
A major driver of both men's and women's migration was the HIV-related death of another adult in the household, confirming prior research in this population: mortality due to HIV is known to have contributed to household instability, precipitating the migration of adults and children (Hosegood et al., 2004a;Ford and Hosegood, 2005;Hosegood and Timaeus, 2005b;Hosegood et al., 2007;Welaga et al., 2009). HIV-related mortality was high in the population during the period considered in this study (Hosegood et al., 2004b), although it began to decline after 2004 . In South African households, the death of an adult member to an HIV-related illness can be catastrophic, stimulating the migration of other adults and children for a variety of reasons. People living with HIV migrate to be cared for or to live near the health services they need (Welaga et al., 2009). 11 The burden of women as caregivers in the epidemic is welldocumented; however, gender norms related to caregiving may be changing. 12 For health and social research and policy, close attention to the gender dimensions of mobility, and to the potential gender biases in conventional measures and data sources, will be needed: women's shorter-distance, shorter-term movements may be less easily measured or predicted than men's, with important implications for service planning and delivery. Promising new approaches may include time-location sampling strategies (for example, Stueve et al., 2001;Magnani et al., 2005;MacKellar et al., 2007) in key migration destinations and utilisation of cell phone technologies to track and communicate with clinic populations (Lester et al., 2006;Besser, 2010). New advances in the development of measures of complex patterns of mobility may be informative for characterising temporary 'service populations' (Taylor and Bell, 2011) in the era of health interventions such as HIV antiretroviral therapy.
In this context of multigenerational, geographically stretched households and low marriage rates, young womenlike their male counterpartsare on the move to seek opportunities, follow aspirations, and earn income. Gender is intrinsic to the social transformations fueling high levels of internal migration and complex forms of mobility in South Africa, with diverse social, economic, and health consequences.  (Dodson, 2000).

A counter-urbanisation may even be occurring in
South Africa as a result of decreasing standards of living in urban slums, as in other areas in the region (Collinson, 2007;Potts, 1995Potts, , 2005. 3. These are areas of high social instability, characterised by high-density housing and limited infrastructure. They are also typical settings for the informal sector employment (such as street trading, beer brewing, sewing, and other activities) in which women predominate. Hunter noted that since the early 20th century, informal settlements have been known to be places of poverty and transactional sex, but also as places that attracted female migrants, as they were known to allow women 'a certain independence' (Hunter, 2007(Hunter, , 2010. 4. One analysis of survey data showed that the national percentage of Black women currently married declined from 35 in 1993 to 30 in 1999 (Posel, 2006). Another study comparing 1970 and 1996 census data reported that in KZN, the percentage of those over age 50 years who were never married had risen from 14% to 27% among men and from 5% to 18% among women (Udjo, 2001). 5. In the population of 48,164 adults aged 18 years and older who were members of households on 1 January 2001, 1,966 individuals (4.1%) were members of more than one household on that date. To define these individuals' household characteristics, just one of their households was selected: the household at which they were a resident or had spent the most time in the previous 6 months. 6. Residency is unique to bounded structures, not to households. Therefore, some polygamous men were not only members but also residents of more than one household within a bounded structure at the same time. Where there were multiple memberships of households that were resident at the same bounded structure at the same time, we selected the residence at which the individual spent the most time in the previous 6 months. 7. Few of these individuals actively refused to participate: some had out-migrated after 1 January 2001 and not retained a household membership before the HSE-1 data collection began, some died before HSE-1 data collection began, and some were not found. 8. As described by Little and Rubin (2002), the score specification was estimated using a logit model, that is,ln[Pr(M = 1)/(1 À Pr(M = 1))] = b0 + b1X1i + b2X2i + ⋯ + biXiwhere Xi . . . represents the known covariates of 'participation' in the HSE-1. These included sex, residency status, marital status, and other measures of household composition. The predicted probabilities from this model were the propensity scores. We then weighted the respondents by dividing the mean participation rate by the predictions of the regression; that is, weight = r(mean participated)/Pr(M = 1). The method corresponds to 'inverse probability weighting', another term used in the literature on causal inference methods. 9. These analyses used the most recent demographic information collected prior to (or at same time as) the collection of socio-economic data for each individual who participated in the HSE-1. Where HSE-1 data were missing, the demographic information collected at the earliest visit after 1 January 2001 was used. 10. The social separation of parents and children in this population is common, with many children living with grandparents. A recent study found that only 27% of non-orphans were living with both parents . In a context of low marriage rates, the comembership of fathers with children is much lower than of mothers with children, which reduces the overall percentage of parents sharing household membership with children. This variable indicates whether either the mother or the father was a member of the same household as at least one of their