How Missing Men Lead to Missing Women: Revising Natural Sex Ratios at Birth for the Fragile Male

Estimates of missing women rely critically on estimates of the natural sex-ratio at birth (SRB). Current estimates ignore in utero male fragility, where male conceptions are disproportionately terminated in the presence of maternal stress. Using natality data from the United States, we document large correlations between a wide range of predictors of spontaneous terminations and SRBs, such as education, poverty, age, parity, birth interval, and even month, day, and time of birth. We show that controlling for maternal stress overturns many commonly held beliefs about natural SBRs. By correcting existing age, parity, and interval estimates by employing woman fixed effects, we show that there should be more “missing men” at birth than currently observed in many developing nations, implying that globally the number of missing women is underestimated by about 30%, and that 20% of the increased SRBs over the past 50 years are due naturally to the demographic transition.

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