Sen's original argument Sen argued that the disparity in sex ratio across eastern Asian countries like India, China, and Korea when compared to North America and Europe, as seen in 1992, could only be explained by deliberate nutritional and health deprivations against women and female children. These deprivations are caused by cultural mechanisms, such as traditions and values, that vary across countries and even regionally within countries. Due to the inherent bias toward male children in many of these countries, female children, if born despite many instances of sex-selective abortion, are born without the same sense of priority given to men. This is especially true in the medical care given to men and women, as well as prioritizing who gets food in less privileged families, leading to lower survival rates than if both genders were treated equally.
Missing women: adults According to Sen's cooperative conflict model, the relations within the household are characterized by both cooperation and conflict: cooperation in the addition of resources and conflict in the division of resources within the household. These intra-household processes are influenced by perceptions of one's
self-interest, contribution and welfare. One's fall back position is the situation for each party once the bargaining process has failed and also determines the ability of each party to survive outside of the relationship. However, because of sex-selective abortions, the sex ratio at birth in countries with high proportions of missing women have ranged 108.5 in India to 121.2 in Mainland China. This is because families have a preference for sons; a decrease in fertility would mean that families would no longer have children of multiple sexes, but rather a single male child. Furthermore, in a study contrasting India and Bangladesh, researchers found that India's declining fertility caused a large intensification in son preference and thus an increase in the number of missing women, while declining fertility in Bangladesh led to less missing women. Regions with higher rates of Hepatitis 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 mainland 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 mainland 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. 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 less among the later born than among the first born children, suggested that factors other than the disease were involved. 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 0.512, girls born with probability 0.488). 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 phenomena 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.
Oster's theory refuted 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 vast majority of 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 67,000 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.
Other diseases In a 2008 study, Anderson and Ray claim that other diseases may explain the "excess female mortality" across Asia and sub-Saharan Africa. By comparing relative death rates of females to males in developed countries to the country in question, Anderson and Ray find that 37 to 45% of the missing women in mainland China can be traced to pre-birth and infancy stage termination factors, whereas only around 11% of India's missing women were caused by similar factors, pointing to the fact that the loss is spread across different ages. They find that by and large, the main cause for female deaths in India is
cardiovascular disease. "Injuries" is the number two cause of female deaths in India. Both of these causes are far greater than maternal mortality and
abortion of fetuses, though "Injuries" may be directly related to gender discrimination. She claims that a person's vulnerability to HIV depends on their overall health, and as misinformed practices, such as the belief that having sex with a female virgin will cure a male of AIDS, dry sex, and household activities that expose women to diseases contribute to weakening women's immune systems which leads to higher HIV mortality rates. Stillwaggon argues for increased focus on sanitation and nutrition rather than just
abstinence or safe sex. As women become healthier the chances of an infected female transmitting HIV to a male partner decline significantly. suggest that conventional assumptions have been: • there are equal numbers of X and Y chromosomes in mammalian sperms • X and Y stand equal chance of achieving conception • therefore equal number of male and female zygotes are formed, and that • therefore any variation of sex ratio at birth is due to sex selection between conception and birth. James cautions that available scientific evidence stands against the above assumptions and conclusions. He reports that there is an excess of males at birth in almost all human populations, and the natural sex ratio at birth is usually between 102 and 108. However the ratio may deviate significantly from this range for natural reasons such as early marriage and fertility, teenage mothers, average maternal age at birth, paternal age, age gap between father and mother, late births, ethnicity, social and economic stress, warfare, environmental and hormonal effects. This school of scholars support their alternate hypothesis with historical data when modern sex-selection technologies were unavailable, as well as birth sex ratio in sub-regions, and various ethnic groups of developed economies. They suggest that direct abortion data should be collected and studied, instead of drawing conclusions indirectly from sex ratio as Sen and others have done. James's hypothesis is supported by historical birth sex ratio data before technologies for ultrasonographic sex-screening were discovered and commercialized in the 1960s and 1970s, as well by reversed sex ratios currently observed in Africa. Michel Garenne reports that many African nations have, over decades, witnessed birth sex ratios below 100, that is more girls are born than boys.
Angola,
Botswana and
Namibia have reported birth sex ratios between 94 and 99, which is quite different than the presumed 104 to 106 as natural human birth sex ratio.
John Graunt noted that in London over a 35-year period in the 17th century (1628–1662), the birth sex ratio was 1.07; while Korea's historical records suggest a birth sex ratio of 1.13, based on 5 million births, in 1920s over a 10-year period.
Female abduction and sale by United States Forces Korea Evidence has shown that number of missing women may be due to other reasons than sex selective abortions or female migrant work. Specifically, female babies, girls and women have been preyed upon by
human traffickers. Kidnapping and enslavement of women by the ISIS, especially of Yazidi women and other female prisoners also constitute human trafficking. In mainland China families are less willing to sell male babies even though they carry a higher price in the trade. Females born exceeding the one-child policy can be sold to wealthier families while the parents claim selling their female baby is better than other alternatives. Overseas adoption services for Chinese children have been involved in baby trafficking to reap the profits of donations from foreign adopters. One study notes that between 2002 and 2005 approximately 1000 trafficked babies were placed with adopting parents, each baby costing $3000. To keep up supply of orphans for adoption, orphanages and retirement homes hire women as baby traffickers.
Under-reporting As discussed above, an additional cause of the missing women phenomenon is under-reporting—women or girls who actually are in the population, but are not included in population statistics because their parents didn't report their birth or delayed reporting it. ==Consequences==