To control for bias in selecting the hospital controls, consulting rooms for outpatients and ward numbers for healthy women were chosen using random numbers. If no suitable subjects were found in the chosen room/ward, the adjacent room/ward was used instead. This systematic selection process was adopted throughout the entire recruitment period. Another sample of 51 community women was recruited from nine different districts of Hangzhou (nonresponse rate 7.8%). The project was approved by the Chinese hospital authorities and the Human Research Ethics Committee of the researchers’ institution.