Wednesday, March 14, 2018

The Internal and External Validity of the Regression Discontinuity Design: A Meta-Analysis of 15 Within-Study-Comparisons | JPAM Featured Article

Regression discontinuity (RD) is generally acknowledged as the most rigorous non-experimental method for obtaining internally valid impact estimates. The study tests the efficacy of RD by comparing RD causal estimates at the treatment cutoff to those from Randomized Control Trials also estimated at this same cutoff. The study identifies 15 previously completed within-study-comparisons that explicitly examined this issue by assuming the RCT results are unbiased and comparing them to RD results.


Junk Food in Schools and Childhood Obesity

June 5, 2014 09:00 AM

Despite limited empirical evidence, there is growing concern that junk food availability in schools has contributed to the childhood obesity epidemic. In this Spring 2012 JPAM paper entitled Junk Food in Schools and Childhood Obesity, Ashlesha Datar and Nancy Nicosia estimate the effects of junk food availability on body mass index (BMI), obesity, and related outcomes among a national sample of fifth graders.

Unlike previous studies, the authors address the endogeneity of the school food environment by controlling for children's BMI at school entry and estimating instrumental variables regressions that leverage variation in the school's grade span. Datar and Nicosia found that junk food availability does not significantly increase BMI or obesity among this fifth-grade cohort despite the increased likelihood of in-school junk food purchases. The results are robust to alternate measures of junk food availability including school administrator reports of sales during school hours, school administrator reports of competitive food outlets, and children's reports of junk food availability. Moreover, the absence of any effects on overall food consumption and physical activity further support the null findings for BMI and obesity.

Read the entire paper at Wiley Online.


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