Journal of the National Cancer Institute Advance Access published online on March 25, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn066
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© The Author 2008. Published by Oxford University Press.
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Design and Analysis of Group-Randomized Trials in Cancer: A Review of Current Practices
Affiliations of authors: Divisions of Epidemiology (DMM) and Health Behavior and Health Promotion (CMA), College of Public Health, Department of Family Medicine, College of Medicine (JL), and Comprehensive Cancer Center (CMA), The Ohio State University, Columbus, OH; Quantitative Sciences and Data Management Branch, Division of HIV/AIDS Prevention, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, US Centers for Disease Control and Prevention, Atlanta, GA (SLP); Division of Public Health and Environment, RTI International, Research Triangle Park, NC (JLB)
Correspondence to: David M. Murray, PhD, Division of Epidemiology, College of Public Health, The Ohio State University, Columbus, OH (e-mail: dmurray{at}cph.osu.edu).
Background: Previous reviews have identified problems in the design and analysis of group-randomized trials in a number of areas. Similar problems may exist in cancer research, but there have been no comprehensive reviews.
Methods: We searched Medline and PubMed for group-randomized trials focused on cancer prevention and control that were published between 2002 and 2006. We located and reviewed 75 articles to determine whether articles included evidence of taking group randomization into account in establishing the size of the trial, such as reporting the expected intraclass correlation, the group component of variance, or the variance inflation factor. We also examined the analytical approaches to determine their appropriateness.
Results: Only 18 (24%) of the 75 articles documented appropriate methods for sample size calculations. Only 34 (45%) limited their reports to analyses judged to be appropriate. Fully 26 (34%) failed to report any analyses that were judged to be appropriate. The most commonly used inappropriate analysis was an analysis at the individual level that ignored the groups altogether. Nine articles (12%) did not provide sufficient information.
Conclusions: Many investigators who use group-randomized trials in cancer research do not adequately attend to the special design and analytic challenges associated with these trials. Failure to do so can lead to reporting type I errors as real effects, mislead investigators and policy-makers, and slow progress toward control and prevention of cancer. A collaborative effort by investigators, statisticians, and others will be required to ensure that group-randomized trials are planned and analyzed using appropriate methods so that the scientific community can have confidence in the published results.
| CONTEXT AND CAVEATS Prior knowledge Group-randomized trials pose distinct analytic challenges, and the validity of the statistical methods used by investigators in the field of cancer research to analyze these trials was unknown. Study design Group-randomized trials on cancer prevention and control were identified by searching the peer-reviewed literature with sets of key words. Each article was coded according to a set of criteria pertaining to the analytic procedures used and their reporting. Contribution Most reports of group-randomized trials in cancer research analyzed in this study used analytical methods that were inappropriate to the assignment by group or failed to provide sufficient information for their assessment. Most articles did not document appropriate methods for sample size calculations, and many ignored group randomization altogether. Implications Failure to attend to the design and analytic challenges posed by interventions that operate at a group level is likely to cause type I errors to be identified as real effects and mislead investigators. A collaborative effort by investigators, statisticians, and others will be needed to ensure that group-randomized trials are planned and analyzed appropriately. Limitations The study did not critique the trials in terms of more general design and analytic issues that were not specific to group-randomized trials.
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The findings and conclusions in this paper are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.
The funding agencies played no role in the design of the study; the collection, analysis, or interpretation of the data; the decision to submit the manuscript for publication; or the writing of the manuscript.
Manuscript received October 16, 2007; revised January 21, 2008; accepted February 20, 2008.
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J Natl Cancer Inst 2008 100: 452-453.
J Natl Cancer Inst 2008 100: 447.
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