VALIDATION OF CANCER PREVALENCE DATA FROM A POSTAL SURVEY BY COMPARISON WITH CANCER REGISTRY RECORDS

Data on self-reported cancer from a health interview survey carried ou t in 1991 in the southeastern Netherlands by means of a postal questio nnaire (n = 17,940) were validated against records from a population-b ased cancer registry. The sensitivity of the questionnaire was 0.552 ( 95% confidence interval (CI) 0.507-0.597), and the specificity was 0.9 95 (95% CI 0.994-0.996). The survey underestimated cancer prevalence i n the population by 25%. Of the 212 false negative cases, 46% were reg istered with nonmelanoma skin cancer. After the exclusion of nonmelano ma skin cancer from cancer registry records, cancer prevalence was ove restimated by the survey by a negligible 2%. The misclassification of cancer by the postal survey was differential according to age, sex, ed ucation, and degree of urbanization. The survey overestimated cancer p revalence ratios for men versus women, old respondents versus young re spondents, and urban residents versus rural residents. The prevalence ratios for respondents with a low educational level versus those with a high level were underestimated using survey data. These patterns rem ained essentially the same after exclusion of nonmelanoma skin cancer from the cancer registry records. This study shows that both overall c ancer prevalence and differences in cancer prevalence between subgroup s of the population may be biased when health interview survey data ar e used. If explicit attention is paid to nonmelanoma skin cancer in su rvey questions, this might improve the validity of overall cancer prev alence estimates, but not that of comparisons between subgroups of the population.