Intended for healthcare professionals


Case-control studies: measures of risk

BMJ 2013; 346 doi: (Published 22 February 2013) Cite this as: BMJ 2013;346:f1185
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London, UK
  1. p.sedgwick{at}

Researchers investigated the association between the occurrence of genitourinary infections from the month before conception until the end of the first trimester and gastroschisis. A case-control study design was used. The mothers of 505 offspring with gastroschisis were identified as cases and mothers of 4924 healthy live born infants as controls. Women self reported genitourinary infections (urinary tract or sexually transmitted) in a telephone interview. A genitourinary infection was reported by 81 (16%) cases compared with 425 (8.6%) controls.1

Which of the following measures of risk of gastroschisis in relation to the risk factor genitourinary infections can be estimated for the above study?

  • a) Hazard ratio

  • b) Odds ratio

  • c) Relative hazard

  • d) Relative risk


The odds ratio (b) of gastroschisis for the risk factor of genitourinary infections can be calculated for the above case-control study, whereas the hazard ratio (a), relative hazard (c …

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