Published 14 October 2009, doi:10.1136/bmj.b4135
Cite this as: BMJ 2009;339:b4135

Endgames

Statistical question

Case-control studies

Philip Sedgwick, senior lecturer in medical statistics

1 Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London SW17 0RE

p.sedgwick@sgul.ac.uk

The first 150 words of the full text of this article appear below.

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 children were followed up until adulthood, with passive smoking and lung cancer status recorded
d) From the above study results we can conclude that lung cancer in adulthood is associated with passive smoking in childhood

a,d—Answer a is true. In a case-control study, . . . [Full text of this article]


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