Her new NBER paper says:
5. Hepatitis B Does Not Explain Male-Biased Sex Ratios in China
by Emily Oster, Gang Chen
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.
I am impressed. It is always inspiring to see a scientist change her mind because of the facts – Emily Oster originally won renown for (apparently) demonstrating the opposite result.
I know that’s how science is supposed to work, but not often enough, I fear. Here are Levitt and Dubner on the idea that Oster has now disproved for herself. Here is my earlier, mildy critical, article about Emily Oster’s work on AIDS transmission. Here is Daniel Hamermesh on the only-some-what-related subject of replication in economics. Tyler is also impressed.