Per Protocol Vs Itt Analysis Essay

I congratulate CMAJ and Boutis and colleagues for a brilliant research paper.1 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. For missing observations, “last value carried forward” is the recommended method.

Per-protocol analysis is a comparison of treatment groups that includes only those patients who completed the treatment originally allocated. If done alone, this analysis leads to bias.

In noninferiority trials, both intention to treat and per-protocol analysis are recommended; both approaches should support noninferiority. In the article by Boutin and colleagues, intention to treat should have included 50 patients in either group as per randomization or at least 45 in the group with splints (in 4 patients, the diagnosis was wrong) and 50 in the group with casts; this may change the results to indicate a borderline effect. In that article, the analysis was done with 43 patients in the splint group and 49 in the cast group, which appears to be a per-protocol analysis, though it was called an intention-to-treat analysis. Hence, noninferiority can be concluded only after analysis by both approaches.


1. Boutis K, Willan A, Babyn P, et al. Cast versus splint in children with minimally angulated fractures of the distal radius: a randomized controlled trial. CMAJ 2010;182:1507–12 [PMC free article][PubMed]

  1. Philip Sedgwick, reader in medical statistics and medical education1
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

Researchers evaluated the effectiveness of a self management programme for arthritis on the overall function of patients with osteoarthritis in primary care. A randomised controlled trial study design was used. The intervention was attendance at six sessions of self management of arthritis, plus an education booklet. The control group received the education booklet only. Participants were patients aged 50 years or more who had osteoarthritis of the hips or knees (or both) and pain or disability (or both). In total, 812 patients were recruited and randomised to the intervention (n=406) or control (n=406).1

The primary outcome was quality of life, as assessed by the short form health survey (SF-36). Secondary outcomes included physical and psychosocial measures. Outcome measures were recorded by postal questionnaires, collected at baseline and 12 months. Analysis was performed on an intention to treat approach. The researchers reported that the intervention group showed a significant reduction on the anxiety subscore of the hospital anxiety and depression scale at 12 months (mean difference 0.62, 95% confidence interval 0.16 to 1.08). The intervention group also showed a significant improvement on the arthritis self efficacy scale for pain (0.98, 0.07 to 1.89) and self efficacy for other aspects of management (1.58, 0.25 to 2.90). Per protocol analysis produced similar results to the intention to treat analysis with respect to significant findings. It was concluded that the self management of arthritis programme reduced anxiety and improved participants’ perceived self efficacy to manage symptoms, although it had no significant effect on pain, physical functioning, or …

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