Intended for healthcare professionals

Endgames Statistical Question

One sided and two sided hypothesis tests

BMJ 2010; 340 doi: (Published 12 May 2010) Cite this as: BMJ 2010;340:c2458
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London

    Researchers investigated whether vaccination against human papillomavirus (HPV) increased the risk of miscarriage in young women.1 The results of two double blind, multicentre, phase three randomised controlled trials were pooled. Participants had been randomly assigned to receive three doses of bivalent HPV 16/18 VLP vaccine with AS04 adjuvant or hepatitis A vaccine (as control) over six months. The primary outcome was rate of miscarriage after vaccination. Given that a lower miscarriage rate with the HPV vaccine was not a safety concern, a one sided test of statistical significance was performed (P=0.16).

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

    • a) Null hypothesis: In the total population, the rate of miscarriage for HPV vaccine is equal to that for control

    • b) Null hypothesis: In the …

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