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Endgames Statistical Question

Meta-analyses II

BMJ 2011; 341 doi: (Published 19 January 2011) Cite this as: BMJ 2011;341:d229
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Section of Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}

Last week’s question described a meta-analysis of the effectiveness of parenteral corticosteroids for the relief of acute severe migraine headache in adults.1 Seven randomised controlled trials were identified in which single dose parenteral dexamethasone, administered alone or in combination with standard abortive therapy, was compared with placebo or any other standard treatment for acute migraine in adults. For each trial, the relative risk for recurrence of headache within 72 hours was obtained for the dexamethasone treatment arm compared with the placebo arm.2

The results of the meta-analysis were presented in a forest plot (figure). When combined with standard abortive therapy, single dose parenteral dexamethasone was more effective than placebo in reducing the recurrence of acute severe migraine headache in adults within 72 hours (relative risk 0.74, 95% confidence interval 0.60 to 0.90).

Forest plot of the effectiveness of dexamethasone in preventing the recurrence of acute severe migraine headache in adults compared with placebo

Which of the following statements, if any, are true?

  • a) The vertical line in the centre of the forest plot represents the line of no effect

  • b) Each trial contributed equally to the total relative risk

  • c) A relative risk greater than one indicates increased risk of recurrence …

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