China’s “Missing Girls”—Son Preference or Hepatitis B Infections?

Available in: Chinese

China has very large numbers of “missing girls.” Public policies have sought to reduce the son preference which is widely believed to cause this. A recent study suggested that much of this female deficit results from a high prevalence of Hepatitis B infection. If true this would suggest that immunization programs should become the first plank of policy objectives.

Millions of women are “missing” in East and South Asia

The imbalance of sex ratios among children and the associated human and social implications has received increasing attention from scholars, policymakers, and governments. Amartya Sen drew especially vivid attention to this by pointing out that over 100 million women were “missing.” [1].

Both India and China have vigorous public policies in place to encourage parents to view daughters as no less valuable than sons. The assumption underlying such policies is that a strong preference for sons is driving the imbalance in sex ratios.[2].

But in a recent paper, Emily Oster argues that up to 75 percent of the “missing girls” in China can be accounted for by the high prevalence of Hepatitis B infection.[3] If true, this would be especially good news for policy makers in China seeking to address the skewed sex ratios, because implementing a Hepatitis B vaccination campaign is far easier than reducing people’s preference for sons.

Das Gupta found that data from a huge sample of births in China show that the only women with elevated probabilities of bearing a son are those who have already borne daughters (Figure 1).[ 4]

Those who have borne only sons show a mildly elevated probability of the next child being a girl—indicative of a mild preference for having a daughter if the sons are already safely in place.

A study of the sex ratio of aborted fetuses in China confirms that women who have only daughters account for the bulk of the excess of female fetuses among total abortions. These data are consistent with the view that son preference is the predominant explanation for the missing girls.[5]

A similar pattern of son preference is found across Asia, showing that parental discrimination against girls is related to the sex composition of their children.Studies in India, Bangladesh, and the Republic of Korea, based on data from before the availability of sex-selection technology (when households resorted to postnatal discrimination), show excess female child mortality concentrated among girls born into families which already have a girl.[6] 

In the years after sex-selective technology became widely available, the South Asian and Korean data indicate that the use of this technology is strongly correlated with the sex composition of existing children—just as in China.[7]

Across East and South Asia all the indicators—sex ratios at birth, sex ratios of aborted fetuses, and sex ratios of child mortality—show that whether or not girls “go missing” is determined by the sex composition of children in the family into which they are conceived. This suggests that son preference is the predominant factor underlying the missing females.

For Oster’s hypothesis to be consistent with these demographic data, women who have borne a daughter would have to be especially prone to contracting Hepatitis B. Or the disease would have to lead somehow to women first bearing daughters followed by an excess of sons. Either of these scenarios would require a much more complex set of biological factors than Oster suggests.

Is it possible that somehow Hepatitis B works in these very complex ways? The medical evidence suggests that this is not the case.

Medical evidence suggests the impact of Hepatitis B on sex ratios at birth is marginal

Oster’s hypothesis is based on micro-studies indicating that women with Hepatitis B have an elevated probability of having sons.[8] Fortunately, a very large data set from Taiwan (China) permits a robust estimation of the impact of Hepatitis B infection on sex ratios at birth.

Lin and Luoh used a national longitudinal data set collected in Taiwan between 1988 and 1999 to track the sex ratio of births to women whose Hepatitis B infection status was known.[9] They found that Hepatitis B infection raised women’s probability of having a son by only 0.25 percent.

Therefore a 15-percent prevalence of Hepatitis B infection would raise the overall sex ratio at birth from a baseline of 105 to 105.165. The sex ratio at birth for all the births in the data set was 109, so Hepatitis B can account for only a tiny part of the elevation in the overall sex ratio at birth.

Oster states that the prevalence of Hepatitis B in China is around 10-15 percent. Using a 11.24% prevalence rate, she estimates that this should result in a sex ratio at birth of 1.10.[10]

However, the findings from the detailed Taiwan data set indicate that the impact of Hepatitis B infection on the sex ratio at birth is tiny, and that Oster has massively overestimated the effect of Hepatitis B on the sex ratio of births in China.

As elsewhere in Asia, the sex ratio at birth rises with birth order in Taiwan (Figure 2). The medical data set makes it possible to see whether the impact of Hepatitis B infection varies by birth order.

Figure 3 shows that the impact is fairly constant across birth orders. It confirms that the overwhelming factor underlying the elevated overall sex ratio at birth is parents’ increasing desperation to have a son as they reach higher birth orders.

In light of this new information, Oster has now changed the premise of her argument.[11]  She now argues that Hepatitis B may skew the sex ratio of births not through the mother’s infection status ¾ as noted in the original microstudies and in her original paper ¾ but the father’s.

Neither premise explains whyonly women with elevated probabilities of bearing a son are those who have already borne daughters.  Nor is either premise supported by the fact that Sub-Saharan African countries with a high prevalence of Hepatitis B have normal sex ratios at birth.[12]

Changes over time in the extent of female deficit seem consistent with the cultural rather than the biological explanation

In China, sex ratios have fluctuated sharply over the twentieth century, and these fluctuations seem to correspond to resource constraints and ideological shifts (Figure 3).

Sex ratios rose sharply when households were placed under severe resource constraints by the disruption of war in the first half of the century, and by fertility decline in the latter decades of the century, which reduced the number of times parents could “toss the coin” to obtain a son.

By contrast in Mao’s China, an ideology of gender equality backed up by collectivization and control over private lives sharply reduced the scope for households to prioritize resource allocation among its members. This is reflected in relatively normal sex ratios, with a muted rise even during the Great Leap famine.

It is highly implausible that the prevalence of Hepatitis B infection fluctuated in tandem with these political shifts. It appears governments have been correct to assume that son preference is the main factor behind the “missing girls” and to focus their policies on changing the cultural roots of son preference.

The findings, interpretations, and conclusions expressed in this brief are entirely those of the authors. They do not necessarily represent the view of the World Bank, its Executive Directors, or the countries they represent.

MONICA DAS GUPTA is a Senior Social Scientist in the Development Research Group (Human Development & Public Services Team, and Sustainable Rural and Urban Development Team). Her current research involves core public health functions and improving public health service delivery in selected countries in Asia and Africa.

Related Resources

·         Gender action plan at a glance

·         Gender action plan data and monitoring