Repeatability of interview-derived socio-demographic and medical information

In this report, the repeatability of socio-demographic and medical information elicited by means of an interviewer-administered questionnaire is examined. One hundred and seven women who were controls in case-control studies of breast disease were re-interviewed approximately one year after initial interview. Both interviews addressed the same time period, namely that which preceded the first interview. For most of the quantitative variables studied, at least 70% of individuals provided two estimates (original and repeat) which were within one unit of each other. Also, comparison of the categorization of individuals on repeated measurements of qualitative variables (reports of events, operations and habits) revealed that most individuals were categorized consistently. This strong agreement between the original and repeat estimates was also reflected in the relatively high values of the summary measures of agreement (the intraclass correlation coefficient for quantitative variables and the Kappa statistic for qualitative variables) for most of the variables studied. The results of the present study on repeatability complement the results of previous research into the criterion validity of questionnaire-derived information and, taken together, suggest that information of relatively high quality may be obtained from such sources.