Including parent's education, family income, etc.

The ICCE measures child care environment through 13 questions in four subscales: "human stimulation" , "social stimulation", "avoidance of restriction", and "social support". It can be used as a self-report or interview, meaning that it does not necessarily need a home visit. Each item is assessed using a multiple-choice format, and the answer is given a binary score according to the manual (1 = good, 0 = not good or not sure); the overall score is calculated by summing all items in the scale. A higher score indicates a better child care environment.

Chinese parent-child interaction scale (CPCIS): Parent-child interaction was assessed using the Chinese Parent-Child Interaction Scale, a standardized questionnaire, which has been well-validated using Rasch analysis. It has also been shown to have good person-separation reliability (0.82). Parents were asked to indicate the frequency of 12 parent-child interactive activities they engaged in during the past month on a scale of 0-5 (0 = not occurring, 5 = very frequent). The questionnaire measures the quantity of the most common activities of learning related, reading, recreation, and interaction with environment. The total scores added from all activities were used in the analysis.

Children's Sleep Habits Questionnaire (CHSQ) Sleep onset and wake up time in the past weekdays and weekends were collected from a parent reported Children Sleep Habits Questionnaire23 and sleep duration in weekdays and weekends was calculated separately. Daily average sleep duration was calculated using the formula: ([weekday sleep duration×5] + [weekend sleep duration×2])/7.