Working Paper: NBER ID: w24856
Authors: David A. Jaeger; Theodore J. Joyce; Robert Kaestner
Abstract: 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.
Keywords: teen birth rates; reality TV; causal inference; identification strategy
JEL Codes: J13; L82
Edges that are evidenced by causal inference methods are in orange, and the rest are in light blue.
| Cause | Effect |
|---|---|
| 16 and Pregnant (J13) | teen birth rates (J13) |
| differential time trends by racial/ethnic composition (J79) | association between 16 and Pregnant and teen birth rates (J13) |
| unemployment rates (J64) | association between 16 and Pregnant and teen birth rates (J13) |
| trends in birth rates across different demographic groups (J11) | validity of Kearney and Levine's causal claims (C92) |
| significant decline in teen birth rates before 16 and Pregnant aired (J13) | validity of Kearney and Levine's causal claims (C92) |