No evidence of response bias in a populationbased childhood cancer survivor questionnaire survey-Results from the Swiss Childhood Cancer Survivor Study

Purpose: This is the first study to quantify potential nonresponse bias in a childhood cancer survivor questionnaire survey. We describe early and late responders and nonresponders, and estimate nonresponse bias in a nationwide questionnaire survey of survivors. Methods: In the Swiss Childhood Cancer Survivor Study, we compared characteristics of early responders (who answered an initial questionnaire), late responders (who answered after =1 reminder) and nonresponders. Sociodemographic and cancer-related information was available for the whole population from the Swiss Childhood Cancer Registry. We compared observed prevalence of typical outcomes in responders to the expected prevalence in a complete (100% response) representative population we constructed in order to estimate the effect of nonresponse bias. We constructed the complete population using inverse probability of participation weights. Results: Of 2328 survivors, 930 returned the initial questionnaire (40%); 671 returned the questionnaire after =1reminder (29%). Compared to early and late responders, we found that the 727 nonresponders (31%) were more likely male, aged