birth increases dramatically after the first birth, for which the ratios remained steadily within the natural baseline over the 20 year interval between 1980 and 1999. Thus, a large majority of couples appear to accept the outcome of the first pregnancy, whether it is a boy or a girl. If the first child is a girl, and they are able to have a second child, then a couple may take extraordinary steps to assure that the second child is a boy. If a couple already has two or more boys, the sex ratio of higher parity births swings decidedly in a feminine direction. This demographic evidence indicates that while families highly value having male offspring, a secondary norm of having a girl or having some balance in the sexes of children often comes into play. reported a study based on the 1990 census in which they found sex ratios of just 65 or 70 boys per 100 girls for births in families that already had two or more boys. A study by found a similar pattern among both Han and non-Han nationalities in Xinjiang Province: a strong preference for girls in high parity births in families that had already borne two or more boys. This tendency to favour girls in high parity births to couples who had already borne sons was later also noted by Coale and Banister, who suggested as well that once a couple had achieved its goal for the number of males, it was also much more likely to engage in "stopping behavior", i.e., to stop having more children. The long-term disparity has led to a significant gender imbalance or skewing of the sex ratio. As reported by the Canadian Broadcasting Corporation, China has between 32million and 36million more males than would be expected naturally, and this has led to social problems. "Because of a traditional preference for baby boys over girls, the one-child policy is often cited as the cause of China's skewed sex ratio [...] Even the government acknowledges the problem and has expressed concern about the tens of millions of young men who won't be able to find brides and may turn to kidnapping women, sex trafficking, other forms of crime or social unrest." The situation will not improve in the near future. According to the Chinese Academy of Social Sciences, there will be 24 million more men than women of marriageable age by