Participation rates in a case control study: The impact of age, race, and race of interviewer

PURPOSE: Despite concerns about declining participation rates in epidemiologic studies in recent years, relatively few papers have discussed obstacles to recruiting study participants or strategies for optimizing response rates. This report describes factors associated with nonparticipation in a population-based, case-control study of breast cancer and discusses ways to overcome barriers to participation. METHODS: Contact and cooperation rates were calculated for participants in the Carolina Breast Cancer Study (CBCS), stratified by case status, age, race, and race of interviewer. Demographic and breast cancer risk factor characteristics of partial and full responders also were compared. RESULTS: Contact rates and cooperation rates varied by case/control status and demographic characteristics. Contact rates were lower among controls, younger women, and black women. Cooperation rates were lower among controls, older women, and black cases. Cooperation rates were higher among both black and nonblack women when participants and interviewers were concordant on race. CONCLUSIONS: Obstacles to recruitment seem to differ among race and age subgroups, suggesting chat recruitment strategies may need to be tailored to potential participants based upon demographic characteristics. Strategies have been implemented to improve response rates in this and other epidemiologic studies; however, additional research and innovation in this area are needed. Ann Epidemiol 1999;9:188-195. (C) 1999 Elsevier Science Inc. All rights reserved.