With the rapid economic development of the metropolis in China, the population of internal migrants has increased to 247 million in 2015, which accounted for 18% of the total population of China . Internal migrants, including rural-to-urban migrants, were population living in their current residence over six months without a permanent/officially registered residence (hukou) of there . The hukou system divided people into rural and urban residence. The rural-to-urban migrants accounted for 3/4 of the internal migrants in 2014 . Lacking hukou in the destination areas, rural-to-urban migrants always have limited access to a range of social welfare provided by the local government, including housing, stable working, public health care services, and social medical insurance (SMI) [3,4,5,6].
The SMI system in China included the new rural cooperative medical scheme (NRCMS), urban resident-based basic medical insurance (URBMI) and urban employee-based basic medical insurance (UEBMI). URBMI was legal to internal migrants in few cities, 5.2% of migrants were enrolled in the URBMI of destination areas in 2014 . Funded by employers and employees, UEBMI was friendly to the rural-to-urban migrants. In 2014, 23.6% of internal migrants were enrolled in the UEBMI of destination areas . Most rural-to-urban migrants were enrolled in the NRCMS of hometown in 2014. Since the SMI was administrated by the local government, rural-to-urban migrants had much difficulty in transferring their SMI between different areas , thus suffered barriers in the reimbursement of their medical bill in destination areas in 2014. Even for the few cities which accepted the destination areas’ medical bill, rural-to-urban migrants always could receive low reimbursement; and the process was inconvenient and unpleasant . Few cities (Shanghai, Chengdu, Shenzhen, Chongqing, etc.) had tried some special medical insurance for the rural-to-urban migrants from 2002, but the effect is limited. Most of these cities had terminated their special medical insurance before 2014 and continued to rely on the SMI system . In other words, these rural-to-urban migrants enrolled in SMI of hometown always have to return for medical care to receive full reimbursement . Someone has found that rural-to-urban migrants enrolled in UEBMI or URBMI were more likely to use inpatient services in their current residence compared with those enrolled in NRCMS of hometown .
Previous studies on rural-to-urban migrants’ returning home for health care had found that about 37.2% of 188 hospitalised migrants had returned (medical return) . The main reasons for their medical return included the lower reimbursement for the medical cost in the host city, followed by high medical expenditure, and having nobody to take care of themselves .
Similar to rural-to-urban migrants, the medical return was also reported among international immigrant. Previous studies found that many Mexican immigrants living within 100 km of the U.S.-Mexico border had a medical return [11,12,13], as well as those living far away from the border . The reasons for their medical return focused on the cost, medical insurance coverage, access, perceived medical quality, social integration, and preference on health service style [13,14,15,16,17,18,19,20]. Among these factors, medical insurance coverage and social integration were the most important factors. The social integration refers to the process of adapting to a new social environment . Most studies showed a negative association between medical return and medical insurance coverage [13, 15, 16, 22, 23], social integration  and certain indicator of social integration, including language proficiency  and acculturation (measured by generation status) . However, one study found no statistical significance between medical insurance coverage and medical return among Korean-U.S. immigrants. The explanation was that costs and social integration were more effective factors on medical return, and limited coverage of U.S. insurance on treatment would also push the immigrants away . Correspondingly, many qualitative studies found that the maintenance of international immigrants’ original culture (another dimension of social integration ) would attract immigrants to return to seek health care. The reasons were as follows: feeling cultural comfort in homeland [15, 17, 18, 23], preferring the medical style of homeland , and having social connections  or social ties with homeland [23, 26].
Similarly, as the diversity of economic development across the rural and urban areas, rural-to-urban migrants in China also experience various level of social integration, including economic integration, cultural, social adaptation, social structural integration, and self-identity . The economic integration was the fundamental of the social integration, which could be measured by employment status, household income, and housing. The self-identity was the final goal of social integration, which included the permanent settlement intention [27,28,29].
There has been plenty of research on international immigrants’ medical return, but rural-to-urban migrants’ medical return remains under-researched, and we have insufficient knowledge on the association between rural-to-urban migrants’ medical return and SMI or social integration. Although medical return could improve migrants’ access to health service, it also makes the service inconvenient and discontinuous. In this study, we applied the popular model of Anderson’s health behaviour model [30, 31] to analyse potential factors associated with the medical return, which was determined by the access to health service in different areas. Influencing factors in the model were divided into three categories, namely predisposing characteristics, enabling resources, and needs . Some indexes of the three dimensions were also covered by the social integration. For instance, the enabling resources refer to the financial and social resources in hometown or destination areas, such as SMI and household income [20, 31], which also belong to the economic integration.
Based on the Chinese SMI system and previous studies on international immigrants’ medical return, we tested two hypotheses. (1) Rural-to-urban migrants enrolled in NRCMS would need to return in order to get full reimbursement, and thus would more likely to return for inpatient service compared with those enrolled in UEBMI or URBMI of current residence. (2)High social integration would be associated with good access to the social resource in current residence and being satisfied with the destination areas, and thus would attract migrants to use inpatient service at current residence.
Hence, we used data from the National Internal Migrant Dynamic Monitoring Survey (NIMDMS) in 2014 to assess the medical return (for inpatient service) of rural-to-urban migrants and to explore the association between the migrants’ medical return and their SMI type or social integration.