Intended for healthcare professionals

Endgames Statistical Question

Errors when statistical hypothesis testing

BMJ 2010; 340 doi: (Published 05 May 2010) Cite this as: BMJ 2010;340:c2348
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London
  1. p.sedgwick{at}

    A randomised controlled trial evaluated the cost and efficacy of community leg ulcer clinics that used four layer compression bandaging. The control treatment was provision of usual care by district nurses.1 Over the 12 month follow-up, ulcers of patients in the clinic group healed quicker than those in the control group (P=0.03). However, no difference was seen between treatment groups in mean total NHS costs per patient (P=0.89). All statistical tests were two sided, and the critical level of significance was set at 0.05 (5%).

    For each of the scenarios below in the total population, determine whether a correct conclusion (a), type I error (b), or type …

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