NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH
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A Cautionary Tale of Evaluating Identifying Assumptions: Did Reality TV Really Cause a Decline in Teenage Childbearing?

David A. Jaeger, Theodore J. Joyce, Robert Kaestner

NBER Working Paper No. 24856
Issued in July 2018
NBER Program(s):Health Economics, Labor Studies

Evaluating policy changes that occur everywhere at the same time is difficult because of the lack of a clear counterfactual. Hoping to address this problem, researchers often proxy for differential exposure using some observed characteristic in the pre-treatment period. As a cautionary tale of how difficult identification is in such settings, we re-examine the results of an influential paper by Melissa Kearney and Phillip Levine, who found that the MTV program 16 and Pregnant had a substantial impact on teen birth rates. In what amounts to a difference-in-differences approach, they use the pre-treatment levels of MTV viewership across media markets as an instrument. We show that controlling for differential time trends in birth rates by a market’s pre-treatment racial/ethnic composition or unemployment rate causes Kearney and Levine’s results to disappear, invalidating the parallel trends assumption necessary for a causal interpretation. Extending the pre-treatment period and estimating placebo tests, we find evidence of an “effect” long before 16 and Pregnant started broadcasting. Our results highlight the difficulty of drawing causal inferences from national point-in-time policy changes.

This paper was motivated by an earlier NBER working paper. The authors of that paper have posted a response to this paper. Another NBER working paper addresses issues in both of these papers.

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Document Object Identifier (DOI): 10.3386/w24856

 
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