Sex Ratio in China
1 min readSex ratio is the ratio of males to females in a population.The primary sex ratio is the ratio at the time of conception，secondary sex ratio is the ratio at time of birth.In humans the secondary sex ratio is commonly assumed to be 105 boys to 100 girls（which for convenience we shall refer to as a ratio of 105）.In human societies，however，sex ratios at birth or among infants may be considerably skewed by sex-selective abortion and infanticide.
The natural sex ratio at conception is estimated close to 1.05 males/female（this is related to the weight ratio of X to Y chromosomes）.Due to the universally higher life expectancy of females，sex ratio tends to even out in adult population，and result in an excess of females among the elderly（e.g.，the male to female ratio falls from 1.05 for the group aged 15 to 65to 0.70 for the group over 65 in Germany，from 1.00 to 0.72 in the USA，from 1.06 to 0.91 in mainland China and from 1.07 to 1.02 in India）.
In the United States，the sex ratios at birth over the period 1970-2002 were 105 for the white non-Hispanic population，104 for Mexican Americans，103 for African Americans and Indians，and 107 for mothers of Chinese or Filipino ethnicity.Among European countries ca.2001，the ratios ranged between 104 in Belgium and 107 in Portugal.In the aggregated results of 56 Demographic and Health Surveys in African countries，the ratio is 103，though there is also considerable country-to-country variation.
