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Selvaraj S, Prasad V. Characteristics of Cluster Randomized Trials: Are They Living Up to the Randomized Trial? JAMA Intern Med. 2013;173(4):313–315. doi:10.1001/jamainternmed.2013.1638
Author Affiliations: Feinberg School of Medicine, Northwestern University, Chicago, Illinois (Mr Selvaraj); and Medical Oncology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland (Dr Prasad).
Cluster randomized control trials (RCTs) are a form of prospective study where groups of individuals are allocated to an intervention. They offer the unique advantage of rigorously evaluating practices that cannot feasibly be randomized to the individual—such as public health or quality programs.1 While cluster RCTs can test questions traditional RCTs cannot, the design requires more participants to achieve equivalent statistical power.1 Over the last decade, the number of cluster RCTs have grown dramatically,2 but some researchers remain uncertain of how to interpret this study design.
A recent editorial highlights the debate regarding where to place cluster RCTs in the research hierarchy.3 Two paired articles in a high-impact journal reached different conclusions regarding routine screening and gown and glove precautions for patients with multidrug-resistant bacterial colonization. One article,4 a quasiexperimental before-and-after study, found that the practice worked, while another,5 a multicenter cluster RCT, found no benefit. If an observational study reaches a different result than an RCT, most would conclude the RCT got it right (ie, hormone therapy and cardiovascular risk, beta carotene therapy and cancer prevention). Yet, in the case of contact precautions, the editorial was ambivalent.3 Ambivalence would be reasonable if cluster RCTs are more likely to reach negative conclusions than RCTs. We sought to examine this hypothesis. Herein, we provide a comparison of cluster RCTs and traditional RCTs for the 50 highest-cited articles (to compare high-impact work) and the most recent 50 articles (to compare a random sampling).
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