“…For example, it turns the estimates of physical activity on In addition, we test whether unobserved time-variant factors may account for the impact of physical activity on development by controlling for some important time-variant variables which are potentially associated with our instruments and developmental outcomes at the same time. Specifically, in light of previous findings, including a statistically significant impact of local weather on children's daily time spent on media and travel activities(Nguyen et al 2021b) and some findings of beneficial impacts of media time on child development(Gentzkow & Shapiro 2008;Nieto & Suhrcke 2021), we separately include the individual's daily time spent on media and travel as additional explanatory variables.Estimation results reported in Appendix TableA9(Panels C1 to C3) show that either excluding or controlling for all of the above-mentioned time-varying variables does not change our results in any significant way. Results from these sensitivity checks, when viewed with results of a Sargan-Hansen test about the exogeneity of our instruments reported at the bottom of each panel in Appendix TableA9, suggest that our instruments are not correlated with time-variant unobservable characteristics in the outcome equations Park et al 2020),.…”