Many of you are probably aware of Emily Oster's controversial study on the potential (causal) effects of Hepatitis B on population gender ratios (see here for a non-technical summary). Oster's paper sparked a great debate as to whether the disease could truly explain a significant portion of the gender imbalance in many of the Asian countries, such as China, where the male/female ratios are remarkably large. Oster and Gang Chen recently revisited the Hepatitis B hypothesis as it applies to China. Their findings:
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.
For what it's worth, I applaud Oster, who is clearly a top-flight researcher doing interesting work, for her academic courage and honesty. It's just great to see an example where one's ego does not interfere with his/her quest to learn the Truth. Good lesson for graduate students such as myself.
Furthermore, despite this retraction (at least with respect to China), Oster is not leaving the topic behind. Indeed, the fact that Hepatitis B explains a good deal of the gender imbalance in some countries but not others is intriguing and worthy of further exploration. This is exactly what she is doing this new working paper, which attempts to reconcile the scientific and population evidence on Hep B and sex ratios.
Excellent research on an interesting line of work. I'd be curious to see how this plays out in the future.
[Ed - 5/13/08 - I was recently informed that the Marginal Revolution blog put up a very similar post yesterday on this topic. Just for the record, I wrote this post as soon as I saw Oster's NBER working paper, and prior to me finding out what other blogs had to say. Also, just as an FYI, you might want to check out the comments under said MR post. The discussion there is pretty interesting.]
2 comments:
Glad to know you're not cribbing from others, Atheen, esp given the topic of discussion in this post. Interesting stuff, and as you point out, kudos to Oster for admitting the data doesn't back her; a good example to see indeed.
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