Data and sample
This study used data from Rural Urban Migration in China (RUMiC), which is initiated by a group of researchers at the Australian National University, the University of Queensland and the Beijing Normal University and supported by IZA Institute of Labor Economics. RUMiC consists of three independent surveys: the Urban Household Survey (UHS), the Rural Household Survey (RHS) and the Migrant Household Survey (MHS). The data we applied in the present study is derived from MHS, which collects rich information on household roster and personal characteristics, education and training backgrounds, employment situation, household income and expenditure during migration period. RUMiC covers 15 cities within nine-largest provinces sending and receiving migrants in China, namely, Bengbu, Chengdu, Chongqing, Dongguan, Guangzhou, Hefei, Hangzhou,Luoyang, Nanjing, Ningbo, Shanghai, Shenzen, Wuhan, Wuxi, and Zhengzhou (See Figure1).
About 5000 migrant households were collected in each wave, and the sampling frame of MHS was conducted by RUMiC team to overcome the problem of under-coverage [24].RUMiC established a list of 550,000 migrant workers, from which 5,000 samples were randomly selected.The sampling frame was established on workplaces (rather than residences), all businesses–including street vendors–in randomly selected enumeration areas within defined city boundaries were included. For each city, a sample of migrant workers was randomly selected within each workplace, based on their birth month. The enumerators subsequently conducted face-to-face interviews with migrant workers and their families [25].
RUMiC was launched in 2008, and three waves RUMiC-2008, RUMiC-2009 are available to apply from the IZA Institute of Labor Economics. But only the wave of 2009 collects smoking-related information.
RUMiC-2009 only provide the information of the household members who was living with the respondent, sharing incomes and expenditures at the time of interview, the data on the family members left behind especially the grandparents was not collected. Thus, present study is limited to the nuclear family only with married-couple and their young unmarried children,, which is only defined as a single family nucleus with married-couple and their young children(age≤16). We also drop the incomplete nuclear family samples such as single parent family to ensure the specific split scenario portrayed as split between spouses as well as split between spouse and their children [22]. After deleting the missing samples and outliers, this study obtains 3738 valid migrant samples, which includes about 1995 males and 1743 females in 15 cities (the sample coverage as shown in Table 1)
Ethnics Statement
This study is a secondary analysis based on the data from the from the RUMiC conducted by a group of researchers at the Australian National University, the University of Queensland and the Beijing Normal University and was supported by the Institute for the Study of Labor (IZA),all of which were subject to multiple stages of reviews by experts to address methodological, ethical and legal issues related to data collection. Final approvals of all RUMIC surveys were required from the Research Ethics Committee of National Bureau of Statistics of China to ensure that the data collection complied with ethical requirement according to the Statistics Act.
Measures
In the RUMiC, rural migrants are defined as rural laborers who move from rural areas to urban destinations within China. Internal migrants currently work in the surveyed cities but lack a local urban Hukou. The focal variable used in present study is split household, which are defined as the migrants’ household arrangements between origin village and urban destination, includes three forms: sole migration, couple migration and family migration. Following Fan (2001) [22], we define the sole migration as the rural migrants who migrate solely, while both their spouse and children are left behind their hometown. Couple migration refers to migrants who migrate and reside together with their spouse but have no children resided together. Family migration is the household with the couple and all the children reside together at the same destination.
The variable of average cigarettes consumed per day is directly collected form the questionnaire item “How many cigarettes on average do you smoke per day now?”. Daily smoking amount is measured by pack of cigarettes consumed per day, which was calculated by the average cigarettes consumed per day / 20. The smoking prevalence is defined as a dummy variable, which is set equal to 1 if migrants smoke at least 1 cigarette per day and 0 otherwise.
According to previous studies, controlled variables incorporate age (ref= age<25), gender (ref=female), educational attainment (ref= junior middle school or less), monthly income (ref= income<1500), duration (ref=duration<5),industry (ref= others), job status (ref= others), work overtime(ref= no), life satisfaction (ref= dissatisfied ).
Modeling strategy
All the analyses are conducted using the Stata 15.0. The Pearson chi-square tests are applied to examine the association between split household, controls and smoking prevalence.
Logit regression analyses are performed to explore the relationship between split household and smoking prevalence, while the demographic variables, employment traits as well as the life satisfaction and city dummies are incorporated as the controls. Tobit estimation on the Daily smoking amount was conducted to give a robust check. OLS regression is applied to discuss the potential transmitted channel linking split household and the smoking prevalence.