Background: The reproducibility of a self-administered questionnaire on different epidemiological variables was examined in a random sample of a cohort of healthy women from the South Swedish Health Care Region. An identical questionnaire has previously been used for assessment of melanoma risk, in a population-based, matched, case-control study from the same region.
Methods: Repeat questionnaires were completed on two occasions, 1-3 years apart, by 670 randomly selected subjects. In addition, exposure data from a case-control study were used to estimate the effect of misclassification.
Results: Overall, there was a fair to good consistency between the answers on the two occasions for the various epidemiological variables. Exposure variables identified as risk factors for melanoma development were reasonably reproducible. The estimated proportion of agreement, A, ranged from 0.74 to 0.92, the average correct classification rate (assuming common sensitivity and specificity), pi, was > or = 0.85 and the kappa coefficient, kappa, ranged between 0.52 and 0.83. However, the question on number of raised naevi on the arm was an exception since it had a lower test-retest reliability (A = 0.62, pi = 0.77, kappa = 0.40). When using data from the case-control study, the effect of the estimated random misclassification was found to only slightly bias odds ratios toward one.
Conclusion: Our questionnaire, used for assessment for melanoma risk, provided information with fair to good test-retest reliability, and corrected odds ratios were found to be only slightly higher than observed odds ratios.