title: Inconsistent definitions for intention-to-treat in relation to missing outcome data: systematic review of the methods literature.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  We 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%).
  
  
  CONCLUSIONS
  We 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.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Alshurafa
authors.forename: Matthias
authors.initials: M
authors.lastname: Briel
authors.forename: Elie A
authors.initials: EA
authors.lastname: Akl
authors.forename: Ted
authors.initials: T
authors.lastname: Haines
authors.forename: Paul
authors.initials: P
authors.lastname: Moayyedi
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gentles
authors.forename: Lorena
authors.initials: L
authors.lastname: Rios
authors.forename: Chau
authors.initials: C
authors.lastname: Tran
authors.forename: Neera
authors.initials: N
authors.lastname: Bhatnagar
authors.forename: Francois
authors.initials: F
authors.lastname: Lamontagne
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Walter
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
mesh_terms: D057194:Intention to Treat Analysis / Q000379:methods* / Q000592:standards; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design / Q000592:standards*; D015983:Selection Bias; D009626:Terminology as Topic