Equivalence design

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Equivalence trials can be used when the objective is to demonstrate equivalence between two treatments or interventions or non-inferiority of the new intervention to the existing one.  Typically, the new drug or device is expected to match the efficacy of the current one but has advantages with regard to say, costs or side effects.  The conduct of an equivalence trial requires different techniques during the design and analysis compared to the standard superiority trials described in the Trial Protocol Tool.  In particular, standard sample size calculations are not appropriate and an equivalence trial requires more patients than a standard randomised controlled trial.  See Further reading for more details.

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Illustrative example - From the UK Health Technology Assessment Report

Women with a family history of breast cancer were randomised to receive either a nurse counsellor or the standard service in that region.  Equivalence of patient anxiety between the nurse counsellors and the standard service was investigated.  (Wilson BJ, Torrance N, Mollison J et al. Improving the referral process for familial breast cancer counselling : an evaluation of two complementary interventions.  UK NHS Health Technology Assessment Final report, 2003.)

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Further reading

Jones B, Jarvis P, Lewis JA, Ebbut AF.  Trials to assess equivalence: the importance of rigorous methods. BMJ 1996; 313: 36-9. 

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This page was last updated 18th April 2005.