THE USE OF COHORT VS REPEATED CROSS-SECTIONAL SAMPLE SURVEY DATA IN MONITORING CHANGING BREAST-CANCER SCREENING PRACTICES

Background. The method used to select a study sample is a key element in designing a research protocol. This article explores two of the mor e common methods used, focusing on the relative advantages and disadva ntages of each one. Methods. Both cohort and repeated, independent cro ss-sectional surveys were conducted in each of 3 years (1988-1990) in the Awareness of Breast Cancer Screening Project to follow changing br east cancer screening rates among a population of women 50-75 years of age on Long Island, New York. Results. Both survey methods revealed s tatistically significant increases in self-reports of mammography use. The cohort and repeated cross-sectional survey sample responses to qu estions concerning knowledge, attitudes, and behavior regarding breast cancer screening were comparable. An educational effect of the baseli ne survey itself on the cohort was not seen. Conclusions. Each of the two survey methods has advantages and disadvantages with respect to th e other. The cohort method permits examination of changes in the same individual over time and is less costly and less time-consuming to per form. On the other hand, the cross-sectional method does not suffer fr om cumulative losses in respondents with repeated surveys and better r eflects the changing community. The study findings can be used to guid e the selection of an appropriate survey methodology for monitoring br east cancer screening practices in other settings.