Non-technical Summary
The relationship between physical activity and child development is well-documented, yet the extant literature provides limited causal insight into the amount of physical activity considered optimal for improving any given health or developmental outcome. This paper exploits exogenous variations in local weather conditions observed across random time use diary dates for the same individuals over time to investigate the causal impact of physical activity on a comprehensive set of health, non-cognitive development, and academic outcomes of children and adolescents.
Employing a fixed-effects instrumental variables model to 16-year data from the Longitudinal Study of Australian Children (LSAC) survey, we find physical activity improves most general developmental and behavioural outcomes. Our results also indicate statistically significant and widespread health benefits of being physically active. Identified health benefits include reduced BMI and waist circumference, increased probability of having excellent health, decreased likelihood of having any ongoing condition or using prescribed medicine, and reduced health expenditures. The results further indicate that physical activity offers greater developmental benefits to females. However, we find little evidence suggesting that physical activity fosters improvement in academic development per se.
We also find that physical activity has a non-linear impact on most health and non-cognitive developmental outcomes. Based on this evidence, we calculate “optimal” hours that children and adolescents should spend each day physically active to obtain the maximum health and non-cognitive developmental benefit. Finally, we find our results robust to a series of specification and sensitivity tests, including an over-identification test and controlling for weather conditions recorded on the same day or over the period when development outcomes were assessed. Our findings have potentially important implications for both study methodologies and health policy. For instance, the results emphasize the importance of addressing potential endogeneity and consideration of the non-linear impact of physical activity on developmental outcomes. Moreover, our newly identified “optimal” hours of daily physical activity (ranging between 3.5 to 6.8 hours, depending on the health/development outcome of interest) indicate that most of children and adolescents are not physically active enough to reap the full potential health and non-cognitive developmental benefits. This finding provides higher quality evidence to support physical activity recommendations for children and adolescents and for physical activity interventions to increase physical activity, particularly among young females.