suggesting discrimination factors at work in accordance to Sen's original theories. In sub-Saharan Africa, in contrast to Sen's contention and average statistics, Anderson and Ray find a large number of women are missing. Sen used the sex ratio of 1.022 for sub-Saharan Africa in work done in 2001, to avoid comparing advanced countries to developing ones. Just as Sen believed, in their study they find no evidence to impute the missing women to birth discrimination such as sex-selective abortions or neglect. To account for the high number of young women missing they discovered that HIV/AIDS was the main cause, surpassing malaria and maternal mortality. Anderson and Ray estimated an annual excess female death rate 600,000 due to HIV/AIDS alone. The age groups with the highest numbers of missing women were the 20- to 24- and 25- to 29-year-old ranges. The high prevalence of HIV/AIDS seems to suggest, according to Anderson and Ray, an imbalance in women's access to healthcare as well as different attitudes about sexual and cultural norms. In an article in 2008, Eileen Stillwaggon, showed that higher rates of HIV/AIDS are the consequence of deep-rooted gender inequalities in sub-Saharan Africa. In countries where women cannot own property they are in a more precarious fall-back position, having less bargaining power to "insist on safe sex without risking abandonment" by their husbands. 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. Natural causes to high or low human sex ratio Other scholars question the assumed normal sex ratio, and point to a wealth of historical and geographical data that suggest sex ratios vary naturally over time and place, for reasons not properly understood. William James and others 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