Endgames Statistical Question

Multiple significance tests

BMJ 2010; 340 doi: http://dx.doi.org/10.1136/bmj.c2963 (Published 10 June 2010) Cite this as: BMJ 2010;340:c2963
  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}sgul.ac.uk

    Researchers undertook a randomised controlled trial to assess the effect of zinc supplementation on the severity and duration of diarrhoea caused by cholera in children.1 Children were recruited if they had watery diarrhoea and dark field microscopy examination of stool was positive for Vibrio cholerae (confirmed by stool culture). Children were randomly allocated to zinc supplementation or placebo.

    The table compares the primary outcomes (duration of diarrhoea and stool output) and secondary outcomes for the zinc supplementation and placebo groups. All hypothesis tests were performed using a two sided, independent samples t test, with a 0.05 (5%) critical level of significance. Zinc supplementation was found to reduce the duration and severity of diarrhoea in children with cholera.

    View this table:

    Impact of zinc supplementation on clinical outcomes in children with cholera

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

    • a) A type I error is when the null hypothesis is rejected …

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