Endgames Statistical Question

Hazard ratios

BMJ 2011; 343 doi: http://dx.doi.org/10.1136/bmj.d5918 (Published 21 September 2011) Cite this as: BMJ 2011;343:d5918
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}sgul.ac.uk

Researchers investigated whether BCG revaccination at 19 months of age reduced child mortality. A randomised controlled trial was performed in Guinea-Bissau, west Africa. In total 1437 children were randomised to BCG revaccination and 1434 to no revaccination (controls). All trial participants had been vaccinated at birth and on the day of enrolment had low or no reactivity to tuberculin and were not severely sick.1

Children were followed from 19 months until 5 years of age. During follow-up 77 children died. The hazard ratio of death for the revaccinated children, compared with controls, was 1.2 (95% confidence interval 0.77 to 1.89).

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

  • a) Revaccinated children had a 20% increased risk of death, compared with controls, at any time during follow-up.

  • b) The hazard rate for the revaccination group was assumed to …

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