Population based control selection and nonresponse among case-control studies in cancer research

Purpose To examine response rate reporting in current epidemiology literature and nonresponse bias from a recent population-based case-control study on kidney cancer in Cook County, IL. Methods A literature review and summary of 62 population-based case-control studies on cancer from eight epidemiology and public health journals published during 2000–2004 was conducted to examine response rate reporting, trends in response rates and factors associated with nonresponse. Additionally, the association of nonresponse with age, gender, race (CMS and cases only) and community area was examined from a recently completed case-control study on kidney cancer in Cook County. Results The article review showed lower participation rates among controls from RDD samples, mail interview surveys and for studies on more common forms of cancer. Most articles did not present a final disposition of sample or a formula for calculating response rates. However, a study of the response rates reported in the 62 articles selected showed a decrease in response rates of 10%–15% since the late 1980ʹs. Using data from the Kidney Cancer Study and modified AAPOR response rate formula number 5, defined as all completed interviews (I) divided by the sum of completed interviews (I), partially completed interviews (P), refusals (R), and noncontact (NC) response codes, the response rate was 72% for cases and 49% for controls. An analysis of nonresponse bias among cases showed that participation decreased significantly with age, with an OR of 0.97 for a one year increase (95% CI 0.98 to 0.99) and DMV control participation was higher for members of a community area that was more than 70% black, with an OR of 2.08 (95% CI 1.16 to 2.73). Conclusions Response rate formulas or calculations for population-based case-control studies are not being presented in current epidemiology literature. Furthermore, response rates appear to be declining despite an increase in response effort. Evidence of lower then expected response rates and nonresponse bias of age among cases and community area among controls is present in a recently conducted case-control study on kidney cancer in Cook County, IL.