American Journal of Epidemiology Advance Access published online on April 23, 2007
American Journal of Epidemiology, doi:10.1093/aje/kwm050
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Practice of Epidemiology |
Secular Trends in Response Rates for Controls Selected by Random Digit Dialing in Childhood Cancer Studies: A Report from the Children's Oncology Group
1 Division of Oncology, Children's Hospital of Philadelphia, Philadelphia PA
2 Department of Pediatrics, School of Medicine, University of Pennsylvania, Philadelphia, PA
3 Division of Epidemiology and Clinical Research, Department of Pediatrics, Medical School, University of Minnesota, Minneapolis, MN
4 University of Minnesota Cancer Center, Minneapolis, MN
5 Department of Epidemiology, School of Public Health, University of North Carolina, Chapel Hill, NC
6 Department of Epidemiology and Cancer Control, St. Jude Children's Research Hospital, Memphis, TN
7 Department of Internal Medicine, School of Medicine, University of New Mexico, Albuquerque, NM
8 Department of Medicine, Center for Health Service Research, Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN
Correspondence to Dr. Greta Bunin, Children's Hospital of Philadelphia, 3535 Market Street, Room 1472, Philadelphia, PA 19104 (e-mail: bunin{at}email.chop.edu).
Received for publication September 19, 2006. Accepted for publication January 17, 2007.
Since the mid-1990s, epidemiologists have anecdotally reported difficulty in recruiting controls using random digit dialing (RDD), but few empirical data have been published. From 1982 to 2003, epidemiologists from the Children's Oncology Group conducted 17 case-control studies using RDD controls. Data for calculating RDD and field response rates were available from eight and 13 of these studies, respectively. Over the period of analysis, the contact rate declined 2.5% per year (95% confidence interval (CI): –3.4, –1.6; p = 0.001), from above 90% in the 1980s to 63–69% in the most recent studies. The response rate (the product of the contact and cooperation rates) showed a decline parallel to that of the contact rate (–2.4% per year, 95% CI: –3.2, –1.6; p < 0.001), from above 80% in the 1980s to 50–67% after the mid-1990s. Field response rates appeared to have declined modestly. The overall response rate (the product of the RDD response and field response rates) paralleled that of the RDD response rate and decreased 2.4% per year (95% CI: –2.7, –2.0; p < 0.001). The current low response rates for RDD indicate a substantial potential for selection bias and a need to seek alternative sources of controls.
case-control studies; data collection; epidemiologic methods
Abbreviations: CI, confidence interval; COG, Children's Oncology Group; RDD, random digit dialing; SCA, Survey of Consumer Attitudes
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