Intended for healthcare professionals

Endgames Statistical Question

What is an “n-of-1” trial?

BMJ 2014; 348 doi: (Published 10 April 2014) Cite this as: BMJ 2014;348:g2674
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

Researchers assessed the effectiveness of “n-of-1” trials for the short term choice of drugs for osteoarthritis. The efficacy of sustained release paracetamol was compared with celecoxib in the management of symptoms associated with osteoarthritis. A series of double blind randomised n-of-1 controlled trials using a double dummy design was performed. The intervention was sustained release paracetamol (two 665 mg tablets, three times a day), or celecoxib (200 mg daily, or 200 mg twice a day for those who were already using this dose). Each treatment regimen was taken for two weeks, administered for three treatment cycles. The primary outcome measures included pain, stiffness, and functional limitation scores; preferred treatment; and adverse effects.1

Participants were eligible if they had osteoarthritis in multiple sites, with pain for at least one month. In addition, their pain was severe enough to warrant consideration of the long term use of celecoxib, but the efficacy of this drug was in doubt. In total, 59 patients were recruited, with 41 completing an n-of-1 trial. It was reported that 33 of the 41 patients could not identify a difference between sustained release paracetamol and celecoxib in terms of overall symptom relief. Of the eight patients who were able to identify differences, seven reported better relief with celecoxib and one with sustained release paracetamol. It was concluded that n-of-1 trials …

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