Hepatitis B: the reason why China has higher male-to-female ratio

In many Asian countries the ratio of male to female population is higher than in the West -- as high as 1.07 in China and India, and even higher in Pakistan. Most people blame the parental preference for boys in these countries and one-child policy in China for creating the gender imbalance. Chicago University professor Emily Oster has new explanation, that the sex ratio imbalance is caused by hepatitis B virus that are prevalent in these countries.

Existing medical literature indicates that carriers of the hepatitis B virus have offspring sex ratios as high as 1.55 boys for each girl. Hepatitis B is common in many Asian countries, especially China, where some 10 to 15% of the population is infected.

Professor Oster  finds that hepatitis B can explain about 45% of the “missing women”: around 75% in China, between 20% and 50% in Bangladesh, Egypt, and West Asia, and under 20% in India, Pakistan and Nepal.

For governments that are worrying about potential social unrest and threats created by tens of millions of bachelors, the solution is to vaccinate their people agaisnt Hepatitis B virus, which will naturally bring more girls into the "marriage market".

Hepatitis B and the Case of the Missing Women  (PDF file)
Published in the Journal of Political Economy
Abstract:  In many Asian countries the ratio of male to female population is higher than in the West -- as high as 1.07 in China and India, and even higher in Pakistan. A number of authors (most notably Sen, 1992) have suggested that this imbalance reflects excess female mortality and, as a result, have argued that as many as 100 million women are ``missing. This paper proposes an explanation for much of the observed over-representation of males: the hepatitis B virus. Evidence drawn from the existing medical literature as well as new studies of recent vaccination efforts indicate that carriers of the hepatitis B virus have offspring sex ratios as high as 1.55 boys for each girl. This is strongly supported by cross-country evidence on hepatitis B prevalence and sex ratios at birth. Hepatitis B is common in many Asian countries, especially China, where some 10 to 15% of the population is infected. Using data on viral prevalence by country as well as estimates of the effect of hepatitis on sex ratio drawn from a wide range of sources, I find that hepatitis B can explain about 45% of the missing women: around 75% in China, between 20% and 50% in Bangladesh, Egypt, and West Asia, and under 20% in India, Pakistan and Nepal.