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Inconsistent definitions for intention-to-treat in relation to missing outcome data: systematic review of the methods

Mohamad Alshurafa1, Matthias Briel, Elie A Akl

  • 1Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada.

Plos One
|November 21, 2012
PubMed
Abstract

Insights

There is no agreement on how to define intention to treat (ITT) when there is missing outcome data (MOD). Researchers suggest clearly reporting how complete and missing data are handled in trials.

Area of Science:

  • Clinical Trials Methodology
  • Biostatistics
  • Evidence-Based Medicine

Background:

  • Authors of randomized trial reports have varied views on the relationship between missing outcome data (MOD) and intention to treat (ITT).
  • Lack of consensus complicates the consistent application and interpretation of ITT principles in research.

Purpose of the Study:

  • To systematically investigate how methodology articles define ITT in the presence of MOD.
  • To examine recommended strategies for handling MOD within an ITT framework.
  • To propose improvements for defining and using ITT concerning MOD.

Main Methods:

  • Systematic search of MEDLINE for methodological articles discussing ITT and MOD.
  • Inclusion criteria focused on articles dedicating substantial text to ITT and MOD.
  • Independent data extraction by two reviewers from eligible articles.

Main Results:

  • Of 66 eligible articles, 55% discussed the relationship between ITT and MOD.
  • Commonly held views included: complete follow-up is required for ITT (58%), ITT and MOD are separate (17%), and ITT requires specific MOD handling strategies (78%).
  • Frequently recommended MOD handling strategies included last outcome carried forward (50%), sensitivity analysis (50%), and imputation (46%).

Conclusions:

  • No consensus exists on the definition of ITT in relation to MOD.
  • Proposes separate reporting of how participants with complete data and those with MOD are handled in randomized trials and systematic reviews for conceptual clarity.

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