⎯ for India, a country which Oster analyzes extensively and if anything the recall bias towards male births would be expected to be higher in India than in Sub-Saharan Africa given the stronger son preference in India. Also odd is the fact that she does not use Garenne’s (2002) compilation and analysis of data on sex ratios at birth from 56 DHS surveys conducted in Sub-Saharan Africa. This covers 29 countries, since several countries had more than one survey spaced some years apart.

Neither Garenne’s compilation of the DHS data nor the UN estimates show high sex ratios at birth in the African countries that Oster lists as having an especially high prevalence of HBV (Table 4). This is another piece of evidence that neither parent’s HepB status makes a significant difference to the sex ratio at birth.

# **III   Conclusions**

The Chinese data strongly support the cultural explanation for the female deficit — namely, that the high sex ratios at birth in China result largely from parental preference for sons. They show that whether or not females “go missing” depends heavily on the existing sex composition of the family into which they are conceived. Girls with no older sisters have similar chances of survival as boys. However, girls conceived in families which already have a daughter experience steeply higher probabilities of being aborted or of dying in early childhood.

The demographic data are very difficult to reconcile with Oster’s hypothesis that most of the imbalance in the sex ratios at birth in China is attributable to the prevalence of hepatitis B. Whether it is via the mother’s infection status or the father’s, the hepatitis B hypothesis is difficult to reconcile with the fact that the **_only_** group of women who have elevated probabilities of bearing a son are those who have already borne daughters.

Indeed, it is difficult to see how any biological hypothesis can explain a significant part of the imbalance in China’s sex ratios at birth ⎯ given the strong relationship between the sex of children already born and the probability of the next child being a boy ⎯ unless it can be shown that the biological factor works in very complex ways such that it selectively affects those women (or men) who have borne girls, or causes them to first bear girls and then boys.

The medical data from Taiwan (China) are very interesting. Firstly, they show that hepatitis B infection raised women’s probability of having a son by only 0.25 percent. Secondly, they show that the effect of HBV status is fairly constant across birth orders even though the sex ratio at birth rises sharply by birth order — suggests strongly that the impact of HBV status is unaffected by the sex composition of previous births. Thirdly, they show that HBV+ status does not selectively affect women who have borne girls — there is no significant _additional_ impact of HBV status on the sex ratio at birth of the third child if the previous children were all female. This seems to rule out the possibility that biological factors can explain the complex patterns found in the demographic data.

Oster’s hypothesis is interesting, but it cannot explain more than a very small part of the totality of the female deficit phenomenon in China. It appears that the governments of these countries have been correct to focus their policies on changing the cultural roots of son preference.

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