Underestimation of subfertility among relatives when using a family history: taboo bias

Family history is widely used in clinical practice and research in order to study genetic aspects of disorders in general, and is recommended as a tool in the assessment of male subfertility. Unfortunately, little is known about the validity of this tool. In this survey, we sent questionnaires to 474 randomly selected men aged 25-40 years in order to collect data on subfertility among them and their relatives. A nonresponder study was also conducted in order to evaluate selection bias. A personal interview was also performed with some respondents in order to gauge how well the data corresponded with questionnaires that were returned. Two hundred forty-three men (51.3%) completed the questionnaire. The responders reported a significantly lower prevalence of subfertility among their relatives than among themselves. Among brothers, the reported prevalence was about 5 times lower (ie, 3.6%) than among responders (15.3%). The nonresponder study and personal interviews showed that these differences were not caused by a selective response to the survey or by the use of a questionnaire instead of a personal interview. We conclude that subfertility among relatives is severely underestimated through the use of family history, probably because of the taboo of discussing subfertility. Knowledge of subfertility may spread selectively within families, causing substantial misclassification. Therefore, researchers and clinicians should be aware that an inquiry of family history is likely to lead to underestimation of subfertility among relatives.