Published 21 October 2009, doi:10.1136/bmj.b4247
Cite this as: BMJ 2009;339:b4247

Endgames

Statistical Question

Screening tests III

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.

The performance of digital mammography as a screening tool for breast cancer was investigated in premenopausal and perimenopausal women. Digital mammography returned a "screen positive" or "screen negative" result. Breast cancer status was diagnosed by biopsy (gold standard). Digital mammography was reported to have a sensitivity of 47%, specificity of 97%, and positive predictive value of 10%.1

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

a) For every 100 women with diagnosed breast cancer, 47 will have had a "screen positive" result.
b) For every 100 women with a "screen positive" result, 47 will have diagnosed breast cancer.
c) For every 100 women without diagnosed breast cancer, 97 will have a "screen negative" result.
d) For every 100 women with a "screen positive" result, 10 will have diagnosed breast cancer.

Answer a is true. Of those women with diagnosed breast cancer, the percentage correctly identified by digital mammography with . . . [Full text of this article]


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