Table 1 Description of family and home environment variables

Socioeconomic status (SES)

Based on mother's or father's occupation (depending on who is highest) using SOC 2000 coding [24]. Divided into three categories: low/medium/high.

Car ownership

Family car ownership. Coding: yes/no.

Number of parents

Number of parents reported as living in the household. Coding: two/less than two (the latter category included the 1% of participants who reported living with neither parent).

Number of siblings

Number of siblings reported living in the household. Coding: 0/1/2/≥3.

Household density

Total number of people reported living in the household divided by the number of bedrooms reported in the house.

Family PA encouragement

Sum of responses (yes/no) to 2 questions about whether family members encourage the child to do physical activity and tell the child that physical activity is good for their health. Based on distribution of responses, dichotomised into high (answered yes to both questions) or low.

Family PA support

Sum of responses (yes/no) to 3 questions about whether family members take the child somewhere to do physical activity, watch the child participate in physical activity and do physical activity with the child. Score range 0-3.¹

Pets

Whether or not child has a pet at home. Coding: yes/no.

Garden

Whether or not child has a garden at home (any outdoor space attached to the home, either for private use or shared with neighbours). Coding: yes/no.

Internet access

Whether or not child has access to the internet at home. Coding: yes/no.

Cable TV

Whether or not child has cable television at home. Coding: yes/no.