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May 20, 1998

Concerns About Run-in Periods in Randomized Trials

Author Affiliations

Margaret A.WinkerMD, Senior EditorIndividualAuthorPhil B.FontanarosaMD, Senior EditorIndividualAuthor

JAMA. 1998;279(19):1526-1527. doi:10-1001/pubs.JAMA-ISSN-0098-7484-279-19-jbk0520

To the Editor.—A potential confounder not addressed by Dr Pablos-Méndez and colleagues1 relates to the interpretation of the placebo response. There is no good evidence that the placebo response is consistent or linear.2,3 In their discussion suggesting that run-in periods that screen for placebo response make for clear criteria, the trials reported assumed linearity and consistency of the placebo response.4 This may allow for a clearer application of inclusion and exclusion criteria but may confound conclusions regarding placebo responders and treatment effect and, therefore, influence results in a positive or negative direction.

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