China’s one child policy is one of the most controversial social policies ever implemented. The policy reduced the fertility rate and has helped raise living standards for most people in China, but it has been heavily criticised for violating human rights and having many negative social consequences, one of which is an excess number of male births.1

In the linked study (doi:10.1136/bmj.b1211), Zhu and colleagues assess trends and geographical patterns in the sex ratio at birth and in people under 20 years of age in China, in addition to the influence of sex selective abortion and the one child policy.2 They find that in 2005 China had more than 32 million excess males under the age of 20, and over 1.1 million excess male births. The authors present a discouraging picture of very high and worsening male to female ratios in the reproductive age group in China for the next two decades.

By showing that sex ratios for different age groups and places of residence vary with how …