Table 1 Definition/codes of the control variables

Predisposing Characteristics

Gender

0 = Male; 1 = Female

Age

Continuous variable

Marital statues

0 = Single; 1 = Partnered

Education

1 = Illiterate; 2 = Primary school and lower; 3 = Junior middle school; 4 = Senior middle school and higher

Enabling Resources

Medical insurance

0 = None; 1 = Yes

Pension

Whether received any pension or not: 0 = No; 1 = Yes

Financial support from children

Financial support received from children: 0 = None; 1 = 0-2000yuan; 2 = 2000-5000yuan; 3 = 5000-10000yuan; 4 = 10000yuan or more

Smoke

0 = No; 1 = Yes

Drink

0 = No; 1 = Yes

Need

Chronic diseases

0 = None; 1 = Yes

Number of ADL limitations

Range from 0 to 6

Number of IADL limitations

Range from 0 to 6

Self-rated health

1 = very good; 2 = good; 3 = fair; 4 = poor; 5 = very poor

Year

2015; 2018