Table 1.

Summary of all the variables in this study

Variable	Study instrument (Definition)	Type of variable
Household
Region	Questionnaire	Categorical (Shanxi, Guizhou)
Single-child family	Questionnaire	Categorical (Yes, No)
Per capita net income	Questionnaire $\left(\frac{\text{Total income}-\text{Total cost of production}}{\text{Number of household members}}\right)$	Continuous (CNY)
Caregiver
Age	Questionnaire	Continuous (Year)
Gender	Questionnaire	Categorical (Male, Female)
Role	Questionnaire	Categorical (Mother, Not mother)
Education	Questionnaire	Categorical (Illiterate, Primary school, Middle school, High school or above)
Depression	Zung Self-rating Depression Scale (Scores >50)	Categorical (Yes, No)
Child
Age	Questionnaire	Continuous (Month)
Gender	Questionnaire	Categorical (Male, Female)
Stunting	WHO Child Growth Standards (Height-for-age Z-score < −2)	Categorical (Yes, No)
Wasting	WHO Child Growth Standards (Weight-for-height Z-score < −2)	Categorical (Yes, No)
Learning material	Questionnaire (Have picture books or toys)	Categorical (Yes, No)
Support for learning	Questionnaire (Engaged four or more activities)	Categorical (Yes, No)
Developmental delay	Age and Stages Questionnaire (Scores of one or more domains fall below the U.S. cut-off points)	Categorical (Yes, No)