100 Million Missing Women

New York Times magazine carries a fascinating report on controversial research that pins at least some of the blame for the developing world's missing women on Hepatitis B virus -- not, as is conventional wisdom, exclusively on gender discrimination.

In a deeply disturbing essay in The New York Review of Books in 1990, the economist and future Nobel laureate Amartya Sen laid bare some brutal math. Because of biological advantages in fighting disease, women typically outnumbered men in fully developed countries, with about 105 women for every 100 men. And yet in developing countries like China and India, there were only about 94 women for every 100 men. The women seemed to have vanished into thin air. What was happening? As a first step toward unraveling the mystery, Sen decided to compute how many women would have been alive in parts of Asia and North Africa had their countries' sex ratios matched those of the developed West. The math shocked the world: more than 100 million women were missing.

In the summer of 2004, a 24-year-old Harvard graduate student in economics named Emily Oster was reading Baruch S. Blumberg's book "Hepatitis B: The Hunt for a Killer Virus." Oster, a tireless number-cruncher, has published research on everything from the decision-making of Powerball players to the correlation between witch trials and rotten weather in Medieval Europe. She was intrigued by several small-scale studies in the Blumberg book that suggested that if either parent was a carrier of the hepatitis B virus, the couple were more likely to have male children. What if nature, wondered Oster, and not the lack of nurture, was behind Sen's 100 million missing women?

Oster crunched the data available for hepatitis B in China, India, Pakistan, Egypt and Bangladesh. Those countries with higher rates of hepatitis B in the 80's, she found, also tended to be the countries with the highest number of missing women. She decided that she had the fuel for what was bound to be a controversial paper.

In December, Oster unveiled her research in The Journal of Political Economy. Working under the assumption that carriers of hepatitis B had 1.5 boys for every 1 girl, she concluded that "hepatitis B can account for about 45 percent of the 'missing women': around 75 percent in China, between 20 and 50 percent in Egypt and western Asia, and under 20 percent in India, Bangladesh, Pakistan and Nepal."