VoxEU Column Development

Missing women in South Asia and China: Biology or discrimination?

More than 100 million women are “missing” in developing countries. A popular paper recently attributed unbalanced sex ratios at birth, particularly in China, to Hepatitis B. This column summarises a large body of evidence refuting that claim. Discrimination, not biology, remains to blame.

In well-known articles published nearly two decades ago, Amartya Sen suggested that more than 100 million women are “missing” in South Asia, East Asia, the Middle East, and North Africa and that they have fallen victim to gender bias in mortality.1 These estimates were refined but largely corroborated by Coale (1991) and Klasen (1994), and a large literature has shown how gender inequality in access to health care, some bias in access to food, and the rising prevalence of sex-selective abortions has contributed to this phenomenon.

Hepatitis B and sex ratios

In 2005, a paper by Emily Oster appeared in the Journal of Political Economy claiming that 47% to 70% of the allegedly “missing” females were never born due to the fact that parents in these countries had high rates of Hepatitis B virus (HVB) carrier status and that carrier status was associated with a higher sex ratio at birth. Thus the “missing” females in South and East Asia were mostly missing as a result of “biology” not “discrimination”. Due to particularly high prevalence of Hepatitis B virus carrier status, the adjustment from “discrimination” to “biology” was particularly strong in China where between 75% and 86% of “missing females” were now due to biology.

While this would have been good news in the sense that the gender bias was not as bad as previously thought, there was some bad news in there as well (though it was not mentioned by Oster). As China, India, Taiwan and other countries with ”missing women” had started immunisation drives against Hepatitis B in the 1980s and 1990s, one would have expected a sharp decline in the sex ratio at birth (and by implication, the overall population sex ratio) and thus a decline in the number of “missing” females. Indeed there was a slight improvement in some countries in South Asia, which had been seen as a genuine decline in discrimination. If Oster was right, this modest improvement was much less than would have been expected as a result of immunisation drives. Thus, according to this argument, gender bias in mortality would be getting worse rather than better everywhere.

Her publication sparked off an intense debate in the literature about the merits of her claims as well evidence that was countering her claim.2 In fact, Oster herself has continued to research the issue and has now, confronted with strong counterevidence by others as well as her own research, retracted the claim that Hepatitis B has a role to play in accounting for the biased sex ratios and the “missing females” in China (and by implication, in South Asia as well).

Why Hepatitis B does not explain missing women

What was the evidence and counterevidence and how are we to interpret these findings? Oster based her claim largely on four pieces of evidence. First, she claimed that the sex ratio at birth in China, and of Chinese immigrants in the United States, has been consistently very high, above the international norm even at a time when sex-selective abortions were unavailable. The second were several micro studies from several parts of the world (none from China or South Asia) that seemed to suggest that the sex ratio at birth was higher when the parents were carriers of the Hepatitis B Virus. The third was time series evidence from Alaskan Natives and Taiwan that immunisation campaigns against Hepatitis B appeared to be associated with a decline in the sex ratio at birth. And the fourth was some cross-country evidence on the link between prevalence rates of carrier status and the sex ratio at birth. Thus, there appeared to be a large amount of evidence of rather diverse character, all supporting her argument.

However, in the subsequent debate, reviewed in Klasen (2008), crucial supporting pieces of evidence appeared to have significant problems and conflicting evidence started to appear. The cross-country evidence was based on rather weak data and appeared to be heavily influenced by observations from countries in South and East Asia where elevated sex ratios at birth could be due to sex-selective under-reporting, female infanticide and neglect, and sex-selective abortions. The micro evidence was suggestive, but it was based on small samples, none came from South and East Asia, and there are nine strains of the HVB virus that are regionally distributed very unevenly. On elevated sex ratios in China, it became clear that sex ratios at birth were perfectly normal in some regions, among first-borns (at least until the 1990s when pre-birth sex selection became increasingly a problem), and in some time periods. Abrevaya (2008) showed that there was strong evidence that the high sex ratio of Chinese immigrants in the United States was indeed also due to sex-selective abortions rather than Hepatitis B virus carrier status. The time series evidence remained suggestive but inconclusive due to a range of empirical problems.

Possibly the most damning evidence came in a recent paper by Ming-Jen Lin and Ming-Ching Luoh (2008), who examined the birth records of over 3 million births in Taiwan and were able to show that the mother’s Hepatitis B virus carrier status had only a tiny impact on the sex ratio at birth. In their calculation, that status can account for less than 2% of the missing women in China, putting the other 98% back in the discrimination column. One possible problem was that it was from Taiwan, not China, and the study was only able to consider the Hepatitis B virus status of the mother, not the father. In follow-up work, Oster and co-authors (2008) examined the births by Hepatitis B virus status of mothers and fathers in a large sample in China and came to the conclusion that the carrier status of either parent did not have a significant impact on the sex ratio at birth. Thus the biased sex ratios and missing females in China (and probably South Asia) are no longer linked to biology, but are, by implication, largely due to discrimination.

The bad news and the good news

What are we to make of this debate? The bad news is that there does not appear to be a biological explanation for about 45% to 70% of “missing females” in China and South Asia. Thus it is still the case that gender discrimination in mortality, through sex-selective abortions and neglect, is as large as presumed by the calculations made by Sen, Coale, and Klasen and Wink. But even in the bad news, there is some good news. Had the original claim been correct, the implication would have been that gender bias in mortality has been getting much worse recently and this was not visible due to the effect of HVB immunisation drives on the sex ratio at birth. Now that this claim no longer seems to hold, the earlier suggestion made by Klasen and Wink (2002, 2003) still seems to be valid: In most parts of the “missing women” regions, there has been a slight to moderate improvement. The exception has been China where the one-child policy, combined with the increasing availability of sex-selective abortions, has lead to a worsened situation for female survival.


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

Blumberg, B. and E. Oster. 2007. Hepatitis B and sex ratios at birth: Fathers or Mothers? Mimeograph, University of Chicago.

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

Chahnazarian, A. B. Blumberg, and W. Th. London. 1988. Hepatitis B and the sex ratio at birth: A comparative study of four populations. Journal of Biosocial Sciences 20: 357-370.

Coale, A. 1991. Excess female mortality and the balance of the sexes: An estimate of the number of missing females. Population and Development Review 17: 517-523.

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.

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

Klasen, S. 1994. Missing Women Reconsidered. World Development 22: 1061-71.

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).

Klasen, S. and C. Wink. 2002. A turning point in gender bias in mortality: An update on the number of missing women. Population and Development Review 28(2): 285-312.

Klasen, S. and C. Wink. 2003. “Missing Women: Revisiting the Debate.” Feminist Economics 9: 263-299.

Klasen, S. 2003. Sex Selection. In P. Demeny, and G. McNicoll (eds.) Encyclopaedia of Population. New York: Macmillan, 878-881.

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. (2006). Hepatitis B and the Case of Missing Women. Journal of Political Economy 113(6) 1163-1216.

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.

Sen, A. 1989. “Women’s Survival as a Development Problem.” Bulletin of the American Academy of Arts and Sciences 43(2):14-29.

Sen, A. 1990. “More than 100 million women are missing.” New York Review of Books, 20 December.


1 Sen (1989, 1990).

2 Das Gupta (2005, 2006), Ebenstein (2008), Lin and Luoh (2008), Abrevaya (2005), Klasen, (2008).

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