Emily Oster on Herself on Hep B and Sex Ratios: I Was Wrong
Hail Emily Oster!
The paper is titled “Hepatitis B Does Not Explain Male-Biased Sex Ratios in China”; here is the abstract:
Earlier work (Oster, 2005) has argued, based on existing medical literature and analysis of cross country data and vaccination programs, that parents who are carriers of hepatitis B have a higher offspring sex ratio (more boys) than non-carrier parents. Further, since a number of Asian countries, China in particular, have high hepatitis B carrier rates, Oster (2005) suggested that hepatitis B could explain a large share (approximately 50%) of Asia’s missing women”. Subsequent work has questioned this conclusion. Most notably, Lin and Luoh (2008) use data from a large cohort of births in Taiwan and find only a very tiny effect of maternal hepatitis carrier status on offspring sex ratio. Although this work is quite conclusive for the case of mothers, it leaves open the possibility that paternal carrier status is driving higher sex offspring sex ratios. To test this, we collected data on the offspring gender for a cohort of 67,000 people in China who are being observed in a prospective cohort study of liver cancer; approximately 15% of these individuals are hepatitis B carriers. In this sample, we find no effect of either maternal or paternal hepatitis B carrier status on offspring sex. Carrier parents are no more likely to have male children than non-carrier parents. This finding leads us to conclude that hepatitis B cannot explain skewed sex ratios in China.
We should hold up Emily Oster as a role model of a truth-seeker. If the abstract does not make it clear, Emily Oster first won her fame by reporting the opposite result about sex ratios. Here are our previous posts on Emily Oster.
A more general lesson, of course, is simply how difficult it is to get at truth. This is a well-defined data set with a (more or less) well-defined answer. Most policy questions aren’t so tractable.
Genuine intellectual curiosity with a triple dose of smarts and a healthy dose of honesty. I hope to see a greater public presence on her part in the future. If she sticks to what she knows and continues to speak straight, her status as a public intellectual could become beyond reproach. Now I need to start a list of people I’ve mentioned these results to to update them.
