Intended for healthcare professionals

Endgames Statistical Question

P values

BMJ 2010; 340 doi: (Published 28 April 2010) Cite this as: BMJ 2010;340:c2203
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London

    A randomised controlled trial evaluated the cost and efficacy of community leg ulcer clinics that used four layer compression bandaging.1 The control treatment was provision of usual care by district nurses. Over the 12 months of follow-up, ulcers healed more quickly among patients randomly assigned to clinic treatment than in those assigned to the control treatment (P=0.03). On the other hand, there was no difference 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%).

    Which of the following statements, if any, can be concluded?

    • a) The P value represents the strength of the evidence in support of the null hypothesis

    • b) There was a statistically significant difference between treatments in healing …

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