To our knowledge, this is the first study using national migrants-based data to examine the sociodemographic disparities in the establishment rate of health records among migrants in China. Our research reveals that the establishment rate of health records among the migrants differed in various sociodemographic characteristics, and heterogeneity existed in establish rate of a certain characteristic.
In terms of sociodemographic characteristics, we found that establishment rate of health records of female were higher than that of male’s. Compared with young immigrants, older immigrants were more likely to establish health records, which was in line with the previous research. This may be the result of the fact that older people had a higher risk of having chronic diseases and worse health status, so they had a stronger motivation to seek health services. In addition, China's BPHS regards the elderly over the age of 65 as a key service group, which may also be the reason for the higher establishment rate of health records among older people.
Compared with the west region, the migrants in the middle region were more likely to establish health records, and the immigrants in the east region were least likely to establish health records. The reason might be that in China, the east part of the country had the most migrants, and the workforce of primary healthcare centers was limited. The professional staff of primary healthcare centers did not have enough time and energy to provide high-quality and enough health services. At the same time, during interviews with the staff of primary healthcare centers, we found that although the remuneration for providing services to each resident was increasing year by year, for some areas with inconvenient transportation, these remunerations may be less than the cost of providing services, which reduced their enthusiasm of providing services . Compared with the migrants with rural household registration, the possibility of establishing health records was higher for migrants with urban household registration. Although in recent years, China is reforming its household registration system and gradually eliminating the differences in public services between urban and rural areas, China's dual household registration system still affects residents' utilization of public health services. In terms of educational attainment, the higher the degree of education was, the higher the possibility of establishing health records was. The reason was probably that education assisted young migrants in gaining a better understanding of the advantages of establishing health records.
As far as migrating characteristics, longer migration time may be related to higher establishing tares of health records. This maybe because that the longer migrants stayed in the place of residence, the more familiar they were with the local health system, and higher the residents' awareness of seeking health services was. Compared with migrants who were migrating for the reason of studying or family issues, people who intended to work or do business were less likely to establish health records. Compared with those who migrated within the province, those who migrated outside the province were less likely to establish health records.
In terms of improving the access of health services, the provision of BPHS is an important measure of the Chinese government. All costs of providing related services are borne by the government, and residents do not have to pay for themselves. In recent years, the Chinese government has also carried out other reforms, such as "family physicians services", which aims to reduce the waiting time for residents to obtain health services and the economic burden of residents improve the efficiency of health services, increase the satisfaction of residents, and improve their health through signing contracts with family physician of primary healthcare centers. Whether it is BPHS or "family physicians service", migrants can get the same services as local residents. However, our research shows that the establishment rate of health records among the migrants remain at a relatively low level, which may hinder the improvement of health equity.
The reasons for the low establishment rate of health records can be analyzed from two aspects. From the supply side, China's health resources are distributed in the shape of "inverted pyramid", which means that health resources are concentrated in secondary and tertiary hospitals. Community health centers have relatively limited health resources. The lack of human resources, coupled with heavy workload of providing BPHS, leading to burnout and high work stress of professional staff, directly affect the provision of BPHS . From the demand side, although BPHS have been implemented for many years, due to the lack of project publicity and health education, migrants' awareness of obtaining BPHS is still relatively low, thus they rarely come to community health centers for BPHS .
The health of the migrants is an important social issue and public policy issue. The establishment of health records strengthens the health management of the migrants, which is an effective way to improve the health of the migrants. Therefore, relevant departments should take actions to promote community health centers to provide more effective and high-quality services, and enhance residents' awareness of health management. Measures should be taken to strengthen health education and health literacy of migrants. At the same time, relative departments should continue to invest in primary healthcare centers to improve their ability to provide better services to meet the needs of residents and migrants.
Our research has several limitations. First, There may be recall bias when participants recalled whether he/she had established a health record, which leads to the underestimation of establishment rate of health records; Second, other factors that may affect the establishment rate of health records (such as family economic status) have not been investigated in the survey, so these variables cannot be included in this study; Third, because this survey is not a continuous survey, this study cannot analyze the long-term trend of establishment rate of health records. However, through 3 years of national survey data, this study provides important basic information and scientific evidence for improving the accessibility of basic public health services and health equity.