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BMJ Endgames

What is a non-inferiority trial?

Philip Sedgwick

Reader in medical statistics and medical education
Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
BMJ 2013;347:f6853

Researchers investigated the effectiveness of cognitive behavioural therapy delivered by telephone compared with the same therapy given face to face in the treatment of obsessive compulsive disorder. A randomised controlled non-inferiority trial study design was used. The intervention was 10 weekly sessions of exposure therapy and response prevention delivered by telephone or face to face. The aim of the study was to investigate whether the delivery of therapy by telephone was as effective as face to face sessions, the standard mode of delivery.

The primary outcome measures included the self report version of the Yale Brown obsessive compulsive disorder checklist measured six months after the completion of treatment. The total score for the checklist ranges from 0 to 40, with higher scores indicating greater obsessive compulsiveness. A prespecified non-inferiority margin of 5 units on the Yale Brown checklist was proposed.

Participants were 72 patients with obsessive compulsive disorder recruited from two psychology outpatient departments. In total, 36 participants were randomised to each treatment group. Using an intention to treat analysis, the difference between treatments (face to face sessions minus telephone) in the Yale Brown checklist score at six months’ follow-up was 0.55 (95% confidence interval 4.26 to 3.15).

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  2. Sedgwick P. What is a superiority trial? BMJ 2013;347:f5420.
  3. Sedgwick P. Absence of evidence is not evidence of absence. BMJ 2011;342:d3126.
  4. Sedgwick P. Confidence intervals and statistical significance: rules of thumb. BMJ 2012;345:e4960.


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This post is based on an article published in "Endgames" an educational series from The BMJ.  Other Endgames articles are available here. Copyright BMJ Publishing Group 2013