The phenomenon of the missing women of Asia is a shortfall in the number of women in Asia relative to the number that would be expected if there was no sex-selective abortion or female infanticide or if the newborn of both sexes received similar levels of health care and nutrition.
The phenomenon was first noted by the Indian Nobel Prize–winning economist Amartya Sen in an essay in The New York Review of Books in 1990, and expanded upon in his subsequent academic work. Sen originally estimated that more than a 100 million women were "missing" (in the sense that their potential existence had been eliminated either through sex selective abortion, infanticide or inadequate nutrition during infancy).
Originally some other economists, notably Emily Oster, questioned Sen's explanation, and argued that the shortfall was due to higher prevalence of the hepatitis B virus in Asia compared to Europe. Further research however, has established that the prevalence of hepatitis B cannot account for more than an insignificant fraction of the missing women." As a result, Sen's explanation for the phenomenon is still the most accepted one.
Background and Sen's original contention
For biological reasons, in absence of human intervention, the ratio of female newborns to male newborns is on average about .95. Subsequent biological development however tends to favor women so that by the time of adolescence the ratio of boys to girls is actually skewed towards women. In Europe and North America the ratio of women to men is becoming greater than 1.05. In Sub Saharan Africa and some of the states in Asia the ratio of women to men is between 1.02 and 1.05.
In contrast, in Punjab the ratio of women to men is .86 and the average for China, South Asia and West Asia is .94. This represents a shortfall of 6% in the number of women if the ratio of one man for one woman is taken as the benchmark and a shortfall of 11% if the more likely 1.05 is the relevant standard.
Translating this into an actual number means that in China alone there are 50 million women "missing" - that should be there but are not. Adding up similar numbers from South and West Asia results in a number of "missing" women higher than 100 million. According to Sen "These numbers tell us, quietly, a terrible story of inequality and neglect leading to the excess mortality of women.".
Emily Oster's former challenge
In her PhD dissertation at Harvard, Emily Oster argued that Sen's hypothesis did not take account of the different rates of prevalence of the Hepatitis B virus between Asia and other parts of the world. Regions with higher rates of Hep B infection tend to have higher ratios of male to female births for biological reasons which are not yet well understood, but which have been extensively documented.
While the disease is fairly uncommon in US and Europe, it is endemic in China and very common in other parts of Asia. Oster argued that this difference in disease prevalence could account for about 45% of the supposed "missing women", and even as high as 75% of the ones in China. Furthermore, Oster showed that the introduction of a Hepatitis B vaccine had a lagged effect of equalizing the gender ratio towards what one would expect if other factors did not play a role.
Oster later published a study with Gang Chen in which she completely dismissed her original hypothesis, asserting Hepatitis B plays no role in forming gender ratio. 
Oster's challenge was met with counter arguments of its own as researchers tried to sort out the available data and control for other possible conflating factors. Avraham Ebenstein questioned Oster's conclusion based on the fact that among first born children the sex ratio is close to the natural one. It is the skewed female-male ratios among second and third born children that account for the bulk of the disparity. In other words, if Hepatitis B was responsible for the skewed ratio then one would expect it to be true among all children, regardless of birth order.
However, the fact that the skewness arose only among the later born but not as much among the first born children, suggested that factors other than the disease were involved.
Monica Das Gupta pointed out that the female-male ratio changed in relation to average household income in a way that was consistent with Sen's hypothesis but not Oster's. In particular, lower household income eventually leads to a higher boy/girl ratio. Furthermore Das Gupta documented that the gender birth order was significantly different conditional on the sex of the first child.
If the first child was male, then the sex of the subsequent children tended to follow the regular, biologically determined sex pattern (boys born with probability .512, girls born with probability .488). However, if the first child was female, the subsequent children had a much higher probability of being male, indicating that conscious parental choice was involved in determining the sex of the child. Neither of these phenomenon can be explained by the prevalence of Hepatitis B.
They are however consistent with Sen's contention that it is purposeful human action - in the form of selective abortion and perhaps even infanticide and female infant neglect - that is the cause of the skewed gender ratio.
Resolution of the debate
Part of the difficulty in discerning between the two competing hypotheses was the fact that while the link between Hepatitis B and a higher likelihood of male birth had been documented, there was little information available on the strength of this link and how it varied by which of the parents were the carriers. Furthermore most prior medical studies did not use a sufficiently high number of observations to convincingly estimate the magnitude of the relationship.
However, in a 2008 study published in the American Economic Review, Lin and Luoh utilized data on almost 3 million births in Taiwan over a long period of time and found that the effect of maternal Hepatitis B infection on the probability of male birth was very small, about one quarter of one percent. This meant that the rates of Hepatitis B infection among mothers could not account for the missing women.
The remaining possibility was that it was the infection among fathers that could lead to a skewed birth ratio. However, Oster, together with Chen, Yu and Lin, in a follow up study to Lin and Luoh examined a data set of 67, 0000 births (15% of whom were Hepatitis B carriers) and found no effect of infection on birth ratio for either the mothers or fathers. As a result Oster retracted her earlier hypothesis. This retraction was praised by the John Bates Clark Medal winner and Freakonomics author Steven Levitt for its honesty.
Monica Das Gupta observed that the preference for boys and the resulting shortage of girls was even more pronounced in the more highly developed Haryana and Punjab regions of India than in poorer areas, and also the high prevalence of this prejudice among the more educated and affluent women (mothers) there. Contrary to the conventional wisdom expectations, in India there are more missing women in developed urban areas, than in backward rural regions. The bias against girls is very evident among the relatively highly developed, middle-class dominated nations (Taiwan, South Korea, Singapore, Armenia, Azerbaijan, Georgia) and the immigrant Asian communities in the United States and Britain. Only recently and in some countries (particularly South Korea) have the development and educational campaigns begun to turn the tide, resulting in more normal gender ratios.
According to Das Gupta's research done in Punjab in the 1980s, girls were not receiving inferior treatment if a girl was born as a first child in a given family, when the parents still had high hopes for obtaining a son later. Subsequent births of girls were however unwelcome, because each such birth diminished a chance of the family having a son. The more affluent and educated women would have fewer offspring, and therefore were under more acute pressure to produce a son as early as possible. As ultrasound imaging and other techniques increasingly allow early prediction of the child's sex, the more affluent families opt for an abortion, or if a girl is born, decrease her chance of survival by, for example, not providing sufficient medical care.
One reason for parents, even mothers, to avoid daughters is the traditional patriarchal culture in the countries where the elimination of females takes place. As parents grow older they can expect much more help and support from their independent sons, than from daughters, who after getting married become in a sense property of their husbands' families, and, even if educated and generating significant income, have limited ability to interact with their natal families. Women are also often practically unable to inherit real estate, so a mother-widow will lose her family's (in reality her late husband's) plot of land and become indigent if she had had only daughters. Poor rural families have meager resources to distribute among their children, which reduces the opportunity to discriminate against girls.
Some research has also noted that in the mid 1990's a reverse began in the observed trends in the regions of Asia where originally the male/female ratios were high. In line with the studies of Monica Das Gupta described above, as income increases the bias in the sex ratio towards boys decreases.
With high per capita income growth in many parts of India and China during the late 1990s and the 2000s, male/female ratios have began shifting towards "normal" levels. However, for India and China, this appears to be due to a fall in adult female mortality rates, relative to male adults, rather than a change in the sex ratio among children and newborns.
A different development occurred in South Korea which in the early 1990s had one of the highest male to female ratios in the world. By 2007 however, South Korea, had a male to female ratio comparable to that found in Western Europe, US and Sub Saharan Africa.
This development characterized both adult ratios as well as the ratios among new births. According to Chung and Das Gupta rapid economic growth and development in South Korea has led to a sweeping change in social attitudes and reduced the preference for sons. Das Gupta, Chung, and Shuzhuo conclude that it is possible that China and India will experience a similar reversal in trend towards normal sex ratio in the near future if their rapid economic development, combined with policies that seek to promote gender equality, continue.. This reversal has been interpreted as the latest phase of a more complex cycle called the "sex ratio transition"..
Czech parasitologist Jaroslav Flegr has found that latent toxoplasmosis infection of mothers can change sex ratio up to 2.6 males per female born. This could, at least partly, explain the phenomenon of missing women.
- Sen, Amartya (20 December 1990). "More Than 100 Million Women Are Missing". New York Review of Books 37 (20). http://ucatlas.ucsc.edu/gender/Sen100M.html.
- "Hepatitis B Does Not Explain Male-Biased Sex Ratios in China". 2008. http://home.uchicago.edu/~eoster/hbvnotecon.pdf. Retrieved 2008-05-21. Cite error: Invalid
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- Template:Cite paper
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