"""""" "' "' J' "_ """\"' I "'\" '"f'_'""'"'" "" """f ' 16 Below is the abstract of a recent National Bureau of Economic Research working paper entitled "Positive and negative mental health consequences of early childhood television watching\" by Waldman et al. (2012}: An extensive literature in medicine investigates the health consequences of early childhood television watching. However, this literature does not address the issue of reverse causation, i.e., does early childhood television watching cause specic health outcomes or do children more likely to have these health outcomes watch more television? This paper uses a natural experiment to investigate the health consequences of early childhood television watching and so is not subject to questions concerning reverse causation. Specically, we use repeated cross-sectional data from 1972 through 1992 on county-level mental retardation rates. countylevel autism rates. and county-level children's cable-television subscription rates to investigate how early childhood television watching affects the prevalence of mental retardation and autism. We nd a strong negative correlation between average county-level cable subscription rates when a birth cohort is below three and subsequent mental retardation diagnosis rates. but a strong positive correlation between the same cable