can help decrease the number of missing women, but the effects of these policy solutions differ greatly between countries due to differing levels of ingrained sexism between cultures. Various international measures have been instituted to combat the problem of missing women. For example, to bring awareness to the problem of missing women, the OECD measures the number of missing women through the "son preference" parameter in its SIGI index. The problem and prevalence According to Amartya Sen, even though women make up the majority of the world's population, the proportion of women in each country's population varies drastically from country to country, with various countries having fewer women than men. This runs contrary to research that females tend to have better survival rates than males, given the same amount of nutritional and medical attention. To capture this divergence from natural sex ratios, the count of "missing women" is measured as a comparison of a country's male-to-female (or female-to-male) sex ratio compared to the natural sex ratio. Unlike female mortality rates, estimates of missing women include counts of sex-specific abortions, which Sen cites as a large factor contributing to the disparity of sex ratios from country to country. Furthermore, female mortality rates fail to account for intergenerational effects from female discrimination, while a comparison of a country's sex ratio to natural sex ratios would. Sen's original research found that while there are typically more women than men in European and North American countries (at around 0.98 men to 1 woman for most countries), the sex ratio of developing countries in Asia, as well as the Middle East, is much higher (in number of males for each female). For example, in Mainland China, the ratio of men to women is 1.06, far higher than most countries. The ratio is much higher than that for those born after 1985, when ultrasound technology became widely available. Using actual numbers, this means that in Mainland 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." Estimates Since Sen's original research, continued research in the field has led to varying estimates on the total numbers of missing women.