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Parallel-Design Double-blind Trials

Chapter:
Study Design and Statistics
Author(s):

AMA Manual of Style Committee

Parallel-Design Double-blind Trials

In this study design, participants are assigned to only 1 treatment group of the study. These trials are generally designed to assess whether 1 or more treatments are superior to the others. Participants and those administering the intervention should all be unaware of which intervention individual participants are receiving (“double-blinding”). Ideally, those rating the outcomes should also be blinded to treatment assignment (“triple-blinding”). Blinded parallel-design trials are often the optimal design to compare 2 or more types of drug or other therapy, since known and unknown potentially confounding factors should be randomly distributed between intervention and control groups. The CONSORT diagram should clearly indicate how many participants were assigned to each treatment group, how many were lost at various stages of the trial, and the reasons that individuals did not complete the trial. Methods of randomization, allocation concealment, and assessment of the success of blinding should be reported. If there is no significant difference between groups, authors cannot claim that the treatments are equivalent; such a conclusion would require an equivalence or noninferiority trial (see 20.2.3, Randomized Controlled Trials, Equivalence and Noninferiority Trials).

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