Intended for healthcare professionals

Endgames Statistical Question

Intention to treat analysis versus per protocol analysis of trial data

BMJ 2015; 350 doi: (Published 06 February 2015) Cite this as: BMJ 2015;350:h681
  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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