Abstract
BackgroundAuthors of randomized trial reports seem to hold a variety of views regarding the relationship between missing outcome data (MOD) and intention to treat (ITT). The objectives of this study were to systematically investigate how authors of methodology articles define ITT in the presence of MOD, how they recommend handling MOD under ITT, and to make a proposal for potential improvement in the definition and use of ITT in relation to MOD.Methods and FindingsWe systematically searched MEDLINE in February 2009 for methodological articles written in English that devoted at least one paragraph to ITT and two other paragraphs to either ITT or MOD. We excluded original trial reports, observational studies, and clinical systematic reviews. Working in teams of two, we independently extracted relevant information from each eligible article. Of 1007 titles and abstracts reviewed, 66 articles met eligibility criteria. Five (8%) did not provide a definition of ITT; 25 (38%) mentioned MOD but did not discuss its relationship to ITT; and 36 (55%) discussed the relationship of MOD with ITT. These 36 articles described one or more of three statements: complete follow-up is required for ITT (58%); ITT and MOD are separate issues (17%); and ITT requires a specific strategy for handling MOD (78%); 17 (47%) endorsed more than one relationship. The most frequently mentioned strategies for handling MOD within ITT were: using the last outcome carried forward (50%); sensitivity analysis (50%); and use of available data to impute missing data (46%).ConclusionWe found that there is no consensus on the definition of ITT in relation to MOD. For conceptual clarity, we suggest that both reports of randomized trials and systematic reviews separately consider and describe how they deal with participants with complete data and those with MOD.
Highlights
Trial methodology experts, systematic review organizations, and authorities including the Consolidated Standards of Reporting Trials (CONSORT), [1] the Cochrane Collaboration, the US Food and Drug Administration, [2] the Nordic Council on Medicine in Europe, [3] and the American Statistical Associations Group [4] have recommended intention to treat (ITT) as the way to analyse randomized controlled trial (RCT) data
We found that there is no consensus on the definition of ITT in relation to missing outcome data (MOD)
We suggest that both reports of randomized trials and systematic reviews separately consider and describe how they deal with participants with complete data and those with MOD
Summary
Systematic review organizations, and authorities including the Consolidated Standards of Reporting Trials (CONSORT), [1] the Cochrane Collaboration, the US Food and Drug Administration, [2] the Nordic Council on Medicine in Europe, [3] and the American Statistical Associations Group [4] have recommended intention to treat (ITT) as the way to analyse randomized controlled trial (RCT) data. A consensus among clinical trialists and methodologists exists about how ITT applies to participants with available outcomes in superiority trials; they should be analysed in the groups to which they were randomized. We hypothesized that authors of methodology articles would hold a heterogeneous view of ITT in relation to MOD, identifying a potential cause of the varying practice in clinical trials and a problem to be solved. Authors of randomized trial reports seem to hold a variety of views regarding the relationship between missing outcome data (MOD) and intention to treat (ITT). The objectives of this study were to systematically investigate how authors of methodology articles define ITT in the presence of MOD, how they recommend handling MOD under ITT, and to make a proposal for potential improvement in the definition and use of ITT in relation to MOD
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