Most prisoners are men. Prisoners worldwide numbered 10.1 million persons on a given day about the year 2010. Among those prisoners, about fifteen men were in prison for every woman in prison.
The sex ratio of prisoners is significant. Punishment is a fundamental political responsibility. Prisoners are among the poorest of the poor in human welfare. Prisoners should be an important public concern. Common human groups such as families and communities usually have a roughly equal sex composition. The sex ratio of prisoners is extremely far from equal.
The sex ratio of prisoners isn’t immutable biological destiny. Across 45 international jurisdictions for which data are available and covering 22% of the world’s 2010 population, the aggregate sex ratio of prisoners fell from 20 men prisoners per woman prisoner to 13 men prisoners per woman prisoner from 1977 to 2010. Data are available from 2003 and 2010 for 177 jurisdictions covering about 94% of the world’s population. From 2003 to 2010, the aggregate prisoner sex ratio fell from 15.7 men in prison per woman in prison to 14.5 men per woman.
Considerable variation exists in the sex ratio of prisoners across the world. Among jurisdictions holding more than 1000 prisoners about 2010, Pakistan had the highest sex ratio: 82 men in prison per woman in prison. India, closely related to Pakistan geographically and historically, had only 23 men in prison per woman in prison. Taiwan was among the jurisdictions closest to sex equality: it had only 4.6 men per woman imprisoned. South Korea, in contrast, had 17.5 men in prison per woman in prison. Most persons would readily notice such sex-ratio differences in ordinary human groups.
The sex ratio of prisoners is relatively high in Sub-Saharan Africa and in low-income countries. Sub-Saharan Africa in aggregate had 30 men in prison per woman in prison about 2010. North America, East Asia, and Pacific had in aggregate 12 men in prisoner per woman in prison. These regional differences correlate with income differences. Low-income jurisdictions had in aggregate 21 men per woman in prison, while the corresponding figure for high-income countries is 12. Even controlling for income group, Sub-Saharan Africa had on average a 55% higher prisoner sex ratio than did East Asia and the Pacific.
Large international differences in the sex ratio among prisoners are not easy to explain. Across 209 international jurisdictions about 2010, the median prisoner sex ratio was 21.2 men in prison per woman in prison. Among those jurisdictions, 25% had a sex ratio less than 14.2, while 25% had a sex ratio greater than 34.7. Indicators for region and income group together explain only 20% of the variation in the logarithm of the sex ratio. Adding to those indicators the urban population share, the labor force participation shares of men and women, and the Human Development Index raises the explained variance only to 34%.
Human biological sex differences, gender, and the socio-economic environment allow large variation in prisoner sex ratios. Considerable variation in prisoner sex ratios exists internationally as well as within particular jurisdictions. High ratios of men in prison per woman in prison are a social justice failure.