Characteristics of telephone survey respondents according to willingness to participate.

When conducting epidemiologic case-control studies, some investigators include only controls who can be interviewed within a certain time after contact and/or do not recontact potential participants who initially refuse, whereas others expend considerable effort to recruit reluctant respondents. This additional effort is only worthwhile if it results in a sample that is more representative of the target population. In this study, the authors used data collected from in-person interviews of 5,616 female controls to compare characteristics of willing, accessible respondents with those of their less accessible or less willing counterparts to determine whether or not the two groups differed with respect to lifestyle, socioeconomic status, health history, and demographic characteristics. Late responders were younger, were more likely to be non-White, were less likely to have attended college, and were more likely to be current smokers than early responders. Initial refusers were similar to late responders with respect to education and race. Initial refusers were also older, were less likely to be currently married, were less likely to have a managerial occupation, had fewer lifetime sexual partners, and were more likely to have a history of diabetes than early responders. These findings suggest that additional effort expended in recruiting reluctant respondents may often result in more accurate estimates of population characteristics that are of interest in epidemiologic research.