*2.2. Measures*

#### 2.2.1. Demographic and Socioeconomic Background

Two waves of demographic data were collected, including gender, age, body-mass index (BMI), household monthly income, and parents' education levels. BMI was calculated from weight and height (kg/m2). Household monthly income was categorized into four levels: (1) *<3000 RMB*; (2) *3000–7000 RMB*; (3) *7000–10,000 RMB*; and (4) >*10,000 RMB*. Parents' educational levels were coded as 1 = *never attended any school*,2= *primary school*, 3 = *junior high school*, 4 = *high school*,5= *junior college or undergraduate*, and 6 = *graduate* (*master or doctor*). According to recommendations in the literature [42], socioeconomic status (SES) scores were calculated by summing standardized scores of the household monthly income level and the parents' education level, whereby high scores indicated high SES. Gender, age, BMI, and SES were utilized as control variables in the analyses described below.
