Healthy Skepticism Library item: 15626

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Publication type: Journal Article

Altman DG.
Missing outcomes in randomized trials: addressing the dilemma
Open Medicine 2009; 3:(2):
http://www.openmedicine.ca/article/view/323/232

Abstract:

Although randomized trials have been conducted for several decades now, some aspects of their analysis remain contentious. Two such issues are what to do about trial participants who do not adhere to the protocol (for example, if they do not receive the intended treatment) and how to deal with those for whom outcome assessments are missing (for example, because they are lost to follow-up). Both of these issues are relevant to the adoption of so-called “intention to treat” (ITT) analysis – a topic that, not surprisingly, also causes debate.

ITT analysis is widely recommended as the preferred approach to analyzing the outcomes of randomized trials.1,2 In an ITT analysis, all randomized patients are included in the analysis in their assigned groups regardless of all considerations, including whether they in fact received the designated intervention. ITT analysis should therefore compare outcomes in groups that correspond exactly to the randomization scheme. Any deviation from that principle may introduce bias.