A systematic review found that deviations from intention-to-treat are common in randomized trials and systematic reviews.

OBJECTIVES: To describe the characteristics, and estimate the incidence, of trials included in systematic reviews deviating from the intention-to-treat (ITT) principle.

STUDY DESIGN AND SETTING: A 5% random sample of reviews were selected (Medline 2006-2010). Trials from reviews were classified based on the ITT: (1) ITT trials (trials reporting standard ITT analyses); (2) modified ITT (mITT) trials (modified ITT; trials deviating from standard ITT); or (3) no ITT trials.

RESULTS: Of 222 reviews, 81 (36%) included at least one mITT trial. Reviews with mITT trials were more likely to contain trials that used placebo, that investigated drugs, and that reported favorable results. The incidence of reviews with mITT trial ranged from 29% (17/58) to 48% (23/48). Of the 2,349 trials, 597 (25.4%) were classified as ITT trials, 323 (13.8%) as mITT trials, and 1,429 (60.8%) as no ITT trials. The mITT trials were more likely to have reported exclusions compared to studies classified as ITT trials and to have received funding.

CONCLUSION: The reporting of the type of ITT may differ according to the clinical area and the type of intervention. Deviation from ITT in randomized controlled trials is a widespread phenomenon that significantly affects systematic reviews.