Participation rates in the selection of population controls in a case-control study of colorectal cancer using two recruitment methods.

OBJECTIVES Low participation rates in the selection of population controls are an increasing concern for the validity of case-control studies worldwide. METHODS We conducted a pilot study to assess two approaches to recruiting population controls in a study of colorectal cancer, including a face-to-face interview and blood sample collection. In the first approach, persons identified through a population roster were invited to participate through a telephone call by an interviewer telephoning on behalf of our research center. In the second approach, individuals were identified from the lists of selected family practitioners and were telephoned on behalf of the family practitioner. RESULTS When the second method was used, participation rates increased from 42% to 57% and the percentage of refusals decreased from 47% to 13%. The reasons for refusing to participate did not differ significantly between the two methods. CONCLUSIONS Contact through the family practitioner yielded higher response rates in population controls in the study area.