November 29, 2018
Professor Emily Oster’s working paper Behavioral Feedback: Do Individual Choices Influence Scientific Results? was published in The National Bureau of Economic Research in November 2018.
In many health domains, we are concerned that observed links - for example, between “healthy” behaviors and good outcomes - are driven by selection into behavior. This paper considers the additional factor that these selection patterns may vary over time. When a particular health behavior becomes more recommended, the take-up of the behavior may be larger among people with other positive health behaviors. Such changes in selection would make it even more difficult to learn about causal effects. Oster formalizes this change in selection in a simple model. She tests for evidence of these patterns in the context of diet and vitamin supplementation. Using both microdata and evidence from published results she shows that selection varies over time with recommendations about behavior and that estimates of the relationship between health outcomes and health behaviors vary over time in the same way. Oster shows that adjustment for selection on observables is insufficient to address the bias. I suggest a possible robustness approach relying on assumptions about proportional selection of observed and unobserved variables.
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