Evaluating Fluctuations in Sex Ratios at Birth in Small Areas

Michele Steinmetz, U.S. Census Bureau
J. Gregory Robinson, U.S. Census Bureau
Heather King, Georgia State University
Daniel Litwok, Michigan State University

Globally, national sex ratios at birth tend to fluctuate very little. However, sex ratios at birth in smaller geographies can fluctuate considerably from year to year. There has been little research to document or understand the magnitude of variations in sex ratios. A reliable evaluation measure could prove to be very helpful in identifying any potential data quality or methodological concerns in such work. Using a theoretical model to calculate probability ranges of sex ratios at birth, this research examines how well actual birth data from several countries over a series of years matched the model’s probability ranges. Initial findings indicate the model can provide meaningful bounds of “statistical significance” in sex ratios at birth. Such models can be a valuable evaluation tool—for example, allowing us to focus on sex ratio outliers that may indicate real data problems rather than those due to random chance.