Hepatitis B and missing women: The rise and decline of a finding

Stephan Klasen

30 August 2008



In late 2005, a paper by Emily Oster, published in the Journal of Political Economy (JPE), claimed that the reason that China (and to some degree South Asian countries) had large female deficits was not gender differences in mortality (pre-and post-birth) – as argued by Amartya Sen and others for years – but the fact that higher prevalence of Hepatitis B carriers there led to naturally higher sex ratios at birth. Around 45% to 70% of the alleged 100 million victims of anti-female discrimination were missing due to this biological relationship. In China it was more than 75%.

The finding made waves. It not only stirred debate in academic circles but was also promoted by Robert Barro in Business Week and Steven Levitt in Slate. The intense academic debate produced at least seven further papers on the subject published in the American Economic Review, the Population and Development Review, and several working papers still in the review process. Most of them criticised particular aspects of the arguments advanced by Oster, with her replying to some of these criticisms.

A few months ago, Emily Oster posted a new paper on her web site with the title “Hepatitis B does not explain male-biased sex ratio in China” where she reports that there is in fact no link between Hepatitis B carrier status and the sex ratio at birth in China (Chen and Oster, 2008). This amounted to a complete retraction of the earlier claim. The details and arguments are summarised in my companion column on Vox and are also available in Klasen (2008). As I just told the story, there is nothing particularly unusual about it – in fact, it could appear as a shining example that the academic community is able to weed out erroneous empirical claims through further research. Moreover, Emily Oster should be commended for not only invariably responding to the many criticisms of her work, but also for undertaking new research to examine these criticisms and then retracting her claim as soon as that research made her original claims untenable.

Troubling timing

But closer inspection of the details and timing of the events leave some open and rather uncomfortable questions. Consider the timing of events. A first draft of the paper, dated 5 February 2005 and labelled “preliminary and incomplete”, was posted on her web site in early February of 2005. Oster was a second-year Ph.D. student at Harvard at the time. The paper was also sent around to people doing research in the field (including me) and several people started providing detailed comments and pointing to some of the weaknesses in the argument.

While this work-in-progress was on-going, Robert Barro took these preliminary and incomplete findings and published a column in Business Week on 28 February 2005, summarising her paper. He claimed that “biology explains a good deal of the missing-women puzzle”, while previously “the presumption was that the excess mortality came from discrimination against women by men and government”. There was no mention of potential problems with the data or the analysis, mostly because at that stage there had been no opportunity to scrutinise these claims at all.

A second version of the paper was produced in March and sent off for publication soon thereafter. Later it became clear that the paper had been submitted to the Journal of Political Economy, then edited by Steven Levitt. In May 2005, while Oster was (according to a message sent to me) still waiting for a first response and referee reports from the JPE, Levitt published, together with Stephen Dubner, a column in the online magazine Slate entitled “The search for 100 million missing women.” There, Levitt described Oster’s arguments and the way she had arrived at them. He stated: “If you believe Oster’s numbers – and as they are presented in a soon-to-be-published [!] paper, they are extremely compelling – then her detective work has established the fate of roughly 50 million of Amartya Sen’s missing women.” Here Levitt, who is both editor of a top economics journal (with very high ranking and associated high rejection rates) and columnist for a general-interest online magazine, clearly mixes his two roles. No wonder that after the pre-announcement in Slate, the paper was then indeed accepted at the JPE later that year and published as the lead article in the last issue of 2005.

That column generated a lot of public discussion about this argument and many of the concerns raised by critics of the claims were then made public as well. In early July 2005, I joined the public discussion and posted a detailed set of comments on the findings on my web site (still available there) which I had previously sent to Oster – they are now appearing in amended fashion as Klasen (2008). In September 2005, the Population and Development Review (PDR), arguably the top journal dealing with demographic issues in developing countries, took the unprecedented step of publishing a criticism of the Oster paper by Monica Das Gupta before Oster’s paper had even been published. That paper focused on a few key weaknesses of the argument, and exchanges between Oster and Das Gupta in the PDR continued in 2005 and 2006.

Similarly, other parts of the evidence were scrutinised by Abrevaya (2008), Ebenstein (2007), and Lin and Luoh (2008). That last paper, which started as a working paper in 2006 and will now be published in the December issue of the American Economic Review, posed a particular challenge to Oster’s claims as it used the data of 3 million women and their off-spring to show that there was no link between mother’s Hepatitis B status and the sex ratio at birth in Taiwan. This was by far the largest data set and most compelling evidence from a country with a “missing women” problem, suggesting that the link was just not there. This paper, as well as persistent criticism of her work, led Oster to undertake further research, extending a large dataset from China to tackle the issue. That research clearly showed that in China there was no link between Hepatitis B and the sex ratio at birth and thus the missing women problem.

Lessons learned

Thus after the three years of intense research, several top-level publications, two entertaining columns, and much public and private discussion, we are just about exactly where we started. We have learned a few things on the way (also about how remarkably quickly some research results make it to the public and into top journals), but maybe a consultation of a Ph.D. thesis by the (late) Anouch Chahnazarian at Princeton, published in 1986, would have obviated the need for all of this. In her dissertation, she examined factors affecting the sex ratio at birth, including the prevalence of Hepatitis B. She concluded by saying that “the negative relationship observed here between birth order and the sex ratio at birth in children of carrier parents fails to provide an explanation of the unusually high sex ratios at birth observed at higher parities in China, a country of high hepatitis B prevalence (p.135).”


Abrevaya, J. 2008. Are there missing girls in the United States? American Economic Review: Applied Economics (forthcoming)

Barro, R. 2005. The case of Asia’s ‘Missing Women’. Business Week, February 28, 2005, p.12.

Chahnazarian, A. 1986. Determinants of the sex ratio at birth. Ph.D. dissertation, Princeton University.

Das Gupta, M. 2005. Explaining Asia’s Missing Women: A new look at the data. Population and Development Review 31(3): 539-535.

Das Gupta, M. 2006. Cultural versus biological factors in explaining Asia’s Missing Women: Response to Oster. Population and Development Review 32: 328-332.

Dubner, S. and S. Levitt . 2005. The search for 100 million missing women. Slate, 24 May 2005.

Ebenstein, Avraham. 2007. Fertility choices and sex selection in Asia: Analysis and Policy. Mimeograph, University of Berkeley.

Klasen, S. 2005. Comments on the Paper by Emily Oster: Hepatitis B and the Case of Missing Women.

Klasen, S. 2008. Missing Women: Some Recent Controversies on Levels and Trends in Gender Bias in Mortality. Ibero America Institute Discussion Paper No. 168. Forthcoming in Basu, K. and R. Kanbur (eds.) Arguments for a better world: Essays in honour of Amartya Sen. Oxford: Oxford University Press (forthcoming).

Lin, M-J. and M-C. Luoh. 2008. Can Hepatitis B mothers account for the number of missing women? Evidence from 3 million newborns in Taiwan. American Economic Review (forthcoming).

Oster, E. (2005). Hepatitis B and the Case of Missing Women. Journal of Political Economy 113(6) 1163-1216.

Oster, E. (2006). On Explaining Asia’s Missing Women: A reply to Das Gupta. Population and Development Review

Oster, E. G. Chen, X. Yu and W. Lin. 2008. Hepatitis B does not explain male-biased sex ratio in China. Mimeographed, University of Chicago.



Topics:  Frontiers of economic research

Tags:  Missing women, Hepatitis B, Steven Levitt, Emily Oster

Professor of Economics, University of Göttingen