Do Fertility Transitions Influence Infant Mortality Declines? Evidence from Early Modern Germany

The timing and sequencing of fertility transitions and early-life mortality declines in historical Western societies indicates that reductions in sibship (number of siblings) may have contributed to improvements in infant health. Surprisingly however, this demographic relationship has received little attention in empirical research. We outline the theoretical difficulties associated with establishing the causal effect of sibship on infant mortality, and provide evidence on the inherent bias associated with conventional empirical approaches. We offer a solution that permits an empirical test of this relationship whilst accounting for reverse causality. Our approach is illustrated by evaluating the causal impact of sibship on infant mortality using genealogical data from 13 German parishes spanning the 16th, 17th, 18th and 19th centuries. Overall, our findings do not support the hypothesis that declining fertility led to increased infant survival probabilities in historical populations.