The data was obtained from the China Migrant Dynamic Survey (CMDS) in 2017 and was provided by the Migrant Population Service Center. CMDS is an annual national sample survey of the internal migrants organized by the NHC from 2009, with an annual sample size of approximately 200,000 households. CMDS adopts the layered, multi-stage, and proportional to scale PPS (Probability proportional to size) sampling method. This study adopted the individual questionnaire A of CMDS, which was uniformly printed and distributed by the NHC. The questionnaire A includes basic information about respondent's demography, perception of the destination, the state of social interaction, and utilization status of NEPHS, etc. Full-time investigators collected the questionnaire data through household interviews, and each respondent gave informed consent before commencing the interview. Dates were entered through the migrant population health and family planning dynamic monitoring system, input data was subjected to multiple checks to ensure quality. The respondents consisted of internal migrants aged 15-59 living in the destination for more than one month. In this study, the inclusion conditions were set as "18-59 years of age, residence duration more than one year. Finally, 138939 people were included in this study. The mean age of the sample was (36.18 ± 9.271) years, and the mean residence duration was (7.21 ± 5.893) years.
AMHE was set as a dependent variable, the question was: have you received MHE in your host community in the past year? Yes = 1 and no = 0.
Social capital was the independent variable of this study. It refers to the resources and benefits received through connections with others, either as individuals or groups. The concept can be broken down into two dimensions: SSC and CSC. SSC refers to the presence of formal opportunity structures or activities in which individuals build or strengthen their social connections. These structures and activities are often operationalized through measures of an individual's civic or social participation. CSC generally refers to individuals' perceptions, beliefs, and attitudes toward their social surroundings, with corresponding measures focused mainly on the concepts of generalized and particularized trust . In this study, social capital was limited to the destination, and it was a localized social capital that reflects the social resources available to the migrant population there.
The SSC of this survey included civic participation and social participation in the destination. Questions of the former were: "since 2016, have you made suggestions to your unit/community/village or supervised the unit/community/village affairs management", "since 2016, have you participated in property donation, blood donation, volunteer activities, etc.", "since 2016, have you reported the situation/put forward policy suggestions to relevant government departments in various ways ", "since 2016, have you posted online comments on national affairs and social events or participated in related discussions", "since 2016, have you participated in party/youth league organization activities and party branch meetings". There were four-level answers for each question: 1= no, 2 = occasionally, 3 = sometimes, and 4 = often, the score ranged from 5 to 20. The question of social participation was "have you participated in any of the following activities in the past year: trade unions, volunteer associations, homecoming associations, fellow-students association, home town chamber of commerce, others", the score ranged from 0 to 7. According to the distribution characteristics of scores, civic participation was integrated into 5 levels: 1(5 points), 2(6 points), 3(7 points), 4(8 points), 5(9-20 points). Social participation was also integrated into 5 levels: 1(0 points), 2(1 points), 3(2 points), 4(3 points), 5(4-6 points). The spearman correlation coefficient of civic participation and social participation was 0.366 (p<0.001), and the SSC grade can be obtained by adding the two grades, and 7 grades were: 1(2 points), 2(3 points), 3(4 points), 4(5 points), 5(6 points), 6(7 points), 7(8-10 points).
The CSC generally referred to IMs' perceptions, beliefs, and attitudes toward their destination in this study, with corresponding measures focused mainly on the concepts particularized trust. There were 5 questions in the survey: "I like the city/place I live now", "I am concerned about the changes in the city/place I live now", "I am very willing to blend with the local people and become a part of them", "I think the local people are willing to accept me as a part of them", "I feel locals look down on outsiders", each question was graded as "totally disagree", "disagree", "basically agree", or "totally agree", α=0.779. According to the distribution of scores, CSC was divided into 7 levels:1(5-14 points), 2(15 points), 3(16 points), 4(17 points), 5(18 points), 6(19 points), 7(20 points).
Moderating variables and controlling variables
LSI and gender were set as moderating variables. The question of LSI was "At present in the local area, does your family have the following difficulties: finding a stable job, affording a house, schools for their children, the income is too low, life is not used to, and other difficulties". These difficulties are thought to be frequently dealt with by migrants. According to the distribution characteristics of scores, LSI was integrated into 3 levels: mild(none), moderate(had 1-2 difficulties), severe(had 3-6 difficulties). Education, migratory range, and community type were set as the control variables. According to the compulsory education years in China, education was divided into two categories: ≤9 and >9 years groups, and the community types were divided into urban and rural areas, the migratory range was divided into inter-province and intra-province.
SPSS 22.0 was used for data analysis. Firstly, we present the descriptive statistical data in order to describe the general characteristics of the included sample. Secondly, we used univariate analysis, AMHE was taken as the dependent variable and other included factors were taken as independent variables for cross-table analysis to investigate whether each factor had a significant impact on the dependent variable, the test index was the chi-square value. Thirdly, we compared differences in CSC and SSC among subgroups of gender and LSI with independent sample t-test and one-way analysis of variance. Fourthly, we used multiple line charts to explore the influence of interaction effects among gender, LSI, CSC and SSC on AMHE. Finally, a hierarchical logistic regression analysis was conducted with AMHE as the dependent variable, CSC, SSC as the independent variables, gender and LSI as the moderating variables, and education, community type and migratory range as the control variables, the aim is to investigate the moderating effects of LSI and gender on the relationship between social capital and AMHE.