Table 1 Variable definitions

 1991

Reference group

 1993

1 if survey conducted at 1993; 0 otherwise

 1997

1 if survey conducted at 1997; 0 otherwise

 2000

1 if survey conducted at 2000; 0 otherwise

 2004

1 if survey conducted at 2004; 0 otherwise

 2006

1 if survey conducted at 2006; 0 otherwise

 2009

1 if survey conducted at 2009; 0 otherwise

 2011

1 if survey conducted at 2011; 0 otherwise

 Urban

Reference group

 Suburban

1 if respondents lived in suburban; 0 otherwise

 Town

1 if respondents lived in town; 0 otherwise

 Rich village

1 if respondents lived in rich village; 0 otherwise

 Poor village

1 if respondents lived in poor village; 0 otherwise

 Quintile1

Reference group

 Quintile2

1 if in the second highest quintile; 0 otherwise

 Quintile3

1 if income in the middle quintile; 0 otherwise

 Quintile4

1 if income in the second lowest quintile; 0 otherwise

 Quintile5

1 if income in the bottom quintile; 0 otherwise

 0~

Reference group

 16~

1 if aged 16–30; 0 otherwise

 31~

1 if aged 31–45; 0 otherwise

 46~

1 if aged 46–60; 0 otherwise

 61~

1 if older than 60; 0 otherwise

 Male

Reference group

 Female

1 if female; 0 otherwise

 Never married

Reference group

 Married

1 if married; 0 otherwise

 Others

1 if divorced, widowed, separated, or unknow; 0 otherwise

 Below primary school

Reference group

 Grad from primary

1 if grad from primary; 0 otherwise

 Junior middle school

1 if grad from junior middle school; 0 otherwise

 Senior middle school or above

1 if grad from senior middle school or above; 0 otherwise

 Yes

Reference group

 No

1 if no insurance; 0 otherwise

 Underweight

Reference group

 Normal weight

1 if 18.5 < = BMI < 26; 0 otherwise

 Overweight

1 if 26 < = BMI < 31; 0 otherwise

 Obese

1 if BMI > = 31; 0 otherwise