Table 1.

Definition and measurement of variables

Variable	Definition and measurement
Whether having given birth to a second birth	whether the second childbirth event occurs
Survival time	the survival time from first childbirth to second childbirth
Fertility intention
Intended number of children	the ideal number of offspring
Presence of son preference	dummy variable: 1= with son preference, 0= without son preference
Individual characteristics
Age	woman’s age at the end of the survey
Age at first childbirth	woman’s age at their first childbirth
Year of first childbirth	dummy variable: 1=1980s and 1990s, 0=2000 and after
Hukou type	dummy variable: 1=rural type, 0= non-rural type
Education	reference category: elementary school and below
Middle school	1=middle school, 0=else
High school/technical secondary school	1=high school/technical secondary school, 0=else
Junior college	1=junior college, 0=else
College and above	1=college and above, 0=else
Existing childbirth status
Gender of first child	dummy variable: 1=male, 0=female
Prior abortion	dummy variable: 1=yes, 0=no
Family environment
Number of paternal siblings	number of paternal siblings,not including self but include siblings who had passed away
Presence of parents-in-law	dummy variable: 1=yes, 0 = no
Regional factor
Region	reference category: Central Shaanxi
Southern Shaanxi	1= Southern Shaanxi, 0=else
Northern Shaanxi	1= Northern Shaanxi, 0=else