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Intent To Treat Analysis

Fig: Mitka et al. JAMA 2012

Determining the sample of participants to be analysed is a crucial step in reporting clinical trials. For such analyses, the gold standard is the “intention-to-treat” principle.

Intention-to-treat analysis is a comparison of the treatment groups that includes all patients as originally allocated after randomization. This is the recommended method in superiority trials to avoid any bias.


  • Retains balance in prognostic factors arising from the original random treatment allocation
  • Gives an unbiased estimate of treatment effect
  • Admits non-compliance and protocol deviations, thus reflecting a real clinical situation

Requirements for an ideal ITT analysis

  • Full compliance with randomised treatment
  • No missing responses
  • Follow-up on all participants


  • Estimate of treatment effect is generally conservative because of dilution due to non-compliance
  • In equivalence trials (attempting to prove that two treatments do not differ by more than a certain amount), this analysis will favour equality of treatments
  • Interpretation becomes difficult if a large proportion of participants cross over to opposite treatment arms
  • Full application of intention to treat is possible only when complete outcome data are available for all randomised subjects

Application of ITT Analysis in clinical trials:

  • About half of all published reports of randomised controlled trials stated that intention to treat was used, but handling of deviations from randomised allocation varied widely.
  • Many trials had some missing data on the primary outcome variable, and methods used to deal with this were generally inadequate, potentially leading to bias.
  • Intention to treat analyses are often inadequately described and inadequately applied.


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