Dynamic Treatment Effect Analysis of TV Effects on Child Cognitive Development

We investigate whether TV watching at ages 6-7 and 8-9 affects cognitive development measured by math and reading scores at ages 8-9 using a rich childhood longitudinal sample from NLSY79. Dynamic panel data models are estimated to handle the unobserved child-specific factor, endogeneity of TV watching, and dynamic nature of the causal relation. A special emphasis is put on the last aspect where TV watching affects cognitive development which in turn affects the future TV watching. When this feedback occurs, it is not straightforward to identify and estimate the TV effect. We adopt estimation methods available in the biostatistics literature which can deal with the feedback feature; we also apply the standard econometric panel data IV approaches. Overall, for math score at ages 8-9, we find that watching TV for more than two hours per day during ages 6-9 has a negative total effect mostly due to a large negative effect of TV watching at the younger ages 6-7. For reading score, there are evidences that TV watching between 2-4 hours per day has a positive effect whereas the effect is negative outside this range. In both cases, however, the effect magnitudes are economically small.