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Table 1 Definitions of variables used

From: Prevalence, correlates, and trajectory of screen viewing among Chinese children in Changsha: a birth cohort study

Baseline characteristics Wave Definition
Time-invariant Wave 1 (children in 12 months)  
Children gender   Male = 1, female = 2
Family member number   Continuous
Pregnant weight (kg)   Continuous
Physical activity in pregnant period (minutes/day)   Continuous
Pregnancy exercise   Yes = 1, no = 2
Pregnancy exercise intensity   Low intensity exercise = 1, moderate exercise = 2
Mother physical activity behavior   Yes = 1, no = 2
Mother physical activity   Low intensity exercise = 1, moderate exercise = 2, heavy exercise = 3
Pregnancy computer use   Yes = 1, no = 2
Pregnancy phone use   Yes = 1, no = 2
Maternal race (Han)   Ethnic Han = 1, not Ethnic Han = 2
Maternal age   Continuous
Educational level   Less than primary school = 1, middle school = 2, high school = 3, university = 4, graduate school = 5, other education = 6
Maternal occupation   Complete collection of Chinese Occupational Classification: class 1 = 1, class 2 = 2, class 3 = 3, class 4 = 4, class 5 = 5, class 6 = 6
Paternal race (Han)   Ethnic Han = 1, not Ethnic Han = 2
Paternal age   Continuous
Educational level   Less than primary school = 1, middle school = 2, high school = 3, university = 4, graduate school = 5, other education = 6
Paternal occupation   Complete collection of Chinese Occupational Classification: class 1 = 1, class 2 = 2, class 3 = 3, class 4 = 4, class 5 = 5, class 6 = 6
Infant weight (kg)   Continuous
Household income (yuan/month)   Less than 2000 yuan/month = 1, 2001–5000 yuan/month = 2, 5001–10,000 yuan/month = 3, 10,001–15,000 yuan/month = 4, More than 15,000 yuan/month = 5
Pregnancy depression   Not depression = 0, depression = 1
Time-variant Wave 1–8 (from children in 12 months to 60 months)  
Children’s daily screen time   Continuous
Children’s daily screen time prevalence   Accept AAP guideline (the reported amount of screen use among children was no more than the recommended screen time of AAP guidelines) = 0, exceed AAP guideline (the reported amount of screen use among children was more than the recommended screen time of AAP guidelines) = 1
Prevalence of children’s interest in screen use   No = 1, occasionally = 2, sometimes = 3, often = 4, always = 5
Children’s daily outdoor activity time   Continuous