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Author Notes:

Corresponding Author: Mark A. Espeland, PhD, Department of Biostatistical Sciences, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157, mespelan@wfubmc.edu


Research Funding:

Look AHEAD is supported by the following cooperative agreements from the National Institutes of Health: DK57136, DK57149, DK56990, DK57177, DK57171, DK57151, DK57182, DK57131, DK57002, DK57078, DK57154, DK57178, DK57219, DK57008, DK57135, and DK56992. The following federal agencies contributed to its support: National Institute of Diabetes and Digestive and Kidney Diseases; National Heart, Lung and Blood Institute; National Institute of Nursing Research, National Center on Minority Health and Health Disparities, Office of Research on Women’s Health, and the Centers for Disease Control and Prevention. The following organizations have committed to make major contributions to Look AHEAD: FedEx Corporation; Health Management Resources; LifeScan, Inc., a Johnson & Johnson Company; Optifast R of Nestle HealthCare Nutrition, Inc.; Hoffmann-La Roche Inc.; Abbott Nutrition; and Slim-Fast Brand of Unilever North America. ACCORD is supported by contract nos. N01-HC-95178, N01-HC-957179, N01-HC-95181, N01-HC-95182, N01-HC-95183, N01-HC-95184, IAA #Y1-HC-9035, and IAA #Y-HC-1010 from the National, Heart, Lung, and Blood Institute, with additional support from the National Institute of Diabetes and Digestive and Kidney Diseases, the National Eye Institute, the National Institute on Aging, the Centers for Disease Control and Prevention and the Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases. General Clinical Research Centers provide support at many sites. Dr. Mount has been supported by U01-DK057136-08S1 from the National Institutes of Diabetes and Digestive and Kidney Diseases.


  • Randomized clinical trials
  • Cross-trial comparisons
  • Type 2 diabetes

Constructing Common Cohorts From Trials with Overlapping Eligibility Criteria: Implications for Comparing Effect Sizes Between Trials

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Journal Title:

Clinical Trials


Volume 6, Number 5


, Pages 416-429

Type of Work:

Article | Post-print: After Peer Review


Background Comparing findings from separate trials is necessary to choose among treatment options, however differences among study cohorts may impede these comparisons. Purpose As a case study, to examine the overlap of study cohorts in two large randomized controlled clinical trials that assess interventions to reduce risk of major cardiovascular disease events in adults with type 2 diabetes in order to explore the feasibility of cross-trial comparisons Methods The Action for Health in Diabetes (Look AHEAD) and The Action to Control Cardiovascular Risk in Diabetes (ACCORD) trials enrolled 5,145 and 10,251 adults with type 2 diabetes, respectively. Look AHEAD assesses the efficacy of an intensive lifestyle intervention designed to produce weight loss; ACCORD tests pharmacological therapies for control of glycemia, hyperlipidemia, and hypertension. Incidence of major cardiovascular disease events is the primary outcome for both trials. A sample was constructed to include participants from each trial who appeared to meet eligibility criteria and be appropriate candidates for the other trial’s interventions. Demographic characteristics, health status, and outcomes of members and non-members of this constructed sample were compared. Results Nearly 80% of Look AHEAD participants were projected to be ineligible for ACCORD; ineligibility was primarily due to better glycemic control or no early history of cardiovascular disease. Approximately 30% of ACCORD participants were projected to be ineligible for Look AHEAD, often for reasons linked to poorer health. The characteristics of participants projected to be jointly eligible for both trials continued to reflect differences between trials according to factors likely linked to retention, adherence, and study outcomes. Limitations Accurate ascertainment of cross-trial eligibility was hampered by differences between protocols. Conclusions Despite several similarities, the Look AHEAD and ACCORD cohorts represent distinct populations. Even within the subsets of participants who appear to be eligible and appropriate candidates for trials of both modes of intervention, differences remained. Direct comparisons of results from separate trials of lifestyle and pharmacologic interventions are compromised by marked differences in enrolled cohorts.

Copyright information:

© The Author(s), 2009

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