Effect of contact letter on control response rates in cancer studies.

Our analysis of response rates for community controls approached in a retrospective study of melanoma indicates that there was an 11 per cent improvement in response rate when the contact letter was changed from inviting participation in a "healthy study" with no mention of cancer to a format which explicitly explained that the study concerned cancer. This improvement was observed for all age-sex groups except younger males. The result suggest that higher response rates may be achieved in studies of cancer if fuller disclosure of the study purposes is made.