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Abstract: A large body of research has
found an association between short birth intervals and the risk of infant
mortality in developing countries, but recent work from highly developed
countries has called these claims into question, arguing that previous
estimates have been biased by a failure to adequately control for unobserved
heterogeneity. This study addresses this issue by estimating within-family
models on a sample of 4.5 million births from 77 countries at various levels of
development. We show that even after controlling for unobserved maternal
heterogeneity, intervals less than 24 months substantially increase the
probability of infant death, and this relationship is present in all countries
in our analysis. We do show, however, that the importance of birth intervals as
a determinant of infant mortality varies inversely with maternal education.
Finally, we demonstrate that the mortality-reducing effects of longer birth
intervals are strong at low levels of development but decline steadily towards
zero as populations become healthier and wealthier. These findings offer a
clear way to reconcile previous research showing that birth intervals are
important for infant mortality in low-income countries, but much less
consequential in high-income settings.