Intended for healthcare professionals

Endgames Statistical question

Case-control studies

BMJ 2009; 339 doi: (Published 14 October 2009) Cite this as: BMJ 2009;339:b4135
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London SW17 0RE
  1. p.sedgwick{at}

    Researchers used a case-control study to investigate whether passive smoking during childhood was associated with lung cancer in adulthood. Passive smoking in childhood was recorded using self completed questionnaires. Participants were recorded as exposed to smoking if anyone smoked regularly where the participant lived as a child. Those individuals with diagnosed lung cancer were more likely to have been exposed to smoking in childhood than those without diagnosed lung cancer (72.8% v 53.4%; P<0.001).1 Which of the following statements, if any, are true?

    • a) Cases are those individuals with diagnosed lung cancer

    • b) Controls are those not exposed to smoking in childhood

    • c) All …

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