From Local to Global: External Validity in a Fertility Natural Experiment

Rajeev Dehejia, Cristian Pop-Eleches, Cyrus Samii

NBER Working Paper No. 21459
Issued in August 2015, Revised in March 2017
NBER Program(s):Children, Development Economics, Labor Studies

We study issues related to external validity for treatment effects using 166 replications of the Angrist and Evans (1998) natural experiment on the effects of sibling sex composition on fertility and labor supply. The replications are based on census data from around the world going back to 1960. We decompose sources of error in predicting treatment effects in external contexts in terms of macro and micro sources of variation. In our empirical setting, we find that macro covariates dominate over micro covariates for reducing errors in predicting treatments, an issue that past studies of external validity have been unable to evaluate. We develop methods for two applications to evidencebased decision-making, including determining where to run the next experiment and whether policy-makers should commission new research or rely on an existing evidence base for making a policy decision.

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Document Object Identifier (DOI): 10.3386/w21459

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