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JAMA Guide to Statistics and Methods
July 2, 2014

The Intention-to-Treat Principle: How to Assess the True Effect of Choosing a Medical Treatment

Author Affiliations
  • 1Berry Consultants LLC, Austin, Texas
  • 2Department of Emergency Medicine, Harbor-UCLA Medical Center; Los Angeles Biomedical Research Institute; and David Geffen School of Medicine at UCLA, Torrance, California
JAMA. 2014;312(1):85-86. doi:10.1001/jama.2014.7523

The intention-to-treat (ITT) principle is a cornerstone in the interpretation of randomized clinical trials (RCTs) conducted with the goal of influencing the selection of medical therapy for well-defined groups of patients. The ITT principle defines both the study population included in the primary efficacy analysis and how the outcomes are analyzed. Under ITT, study participants are analyzed as members of the treatment group to which they were randomized regardless of their adherence to, or whether they received, the intended treatment.1-3 For example, in a trial in which patients are randomized to receive either treatment A or treatment B, a patient may be randomized to receive treatment A but erroneously receive treatment B, or never receive any treatment, or not adhere to treatment A. In all of these situations, the patient would be included in group A when comparing treatment outcomes using an ITT analysis. Eliminating study participants who were randomized but not treated or moving participants between treatment groups according to the treatment they received would violate the ITT principle.