Our case-control study might introduce certain biases. Firstly, the association between tea consumption and ovarian cancer has not been firmly established at the time of interview; therefore, information bias concerning personal habits thus appears unlikely. All of the interviews were conducted by a single investigator (first author) to avoid intra-interview bias. Although tea consumption can be recalled by the participants with reasonable accuracy, misclassification of its exposure level may still exist. However, such random errors are unlikely to influence the observed association between tea drinking and ovarian cancer. The recall between cases and controls may differ because of variations in the perceived reference frame or in subject motivation. Cases were more likely to sustain recall bias, because the onset of the disease might change their personal habits or at least the recall of their habits. Therefore, a fixed recall period (5 years before diagnosis for cases and 5 years before interview for controls) was adopted to avoid possible exposure change relating to case disease status.