Published 27 May 2009, doi:10.1136/bmj.b2077
Cite this as: BMJ 2009;338:b2077

Endgames

Statistical question

Likelihood ratios

John Fletcher, clinical epidemiologist

1 BMJ, London WC1H 9JR

jfletcher@bmj.com

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

In a study of general practice records in the UK, the symptom of dysphagia was found to have a positive likelihood ratio of 300 for oesophageal cancer, which itself had an incidence of 1 case in every 10 000 persons per year. Which of the following statements, if any, are true?

a) Among people with dysphagia, the ratio of those with cancer to those without is 300 to 1
b) Cancer is 300 times more likely in patients with dysphagia than in the general population
c) More than 95% of people with dysphagia seeing their general practitioner will have cancer
d) More than 95% of people with dysphagia seeing their general practitioner will not have cancer

b, d—Answer b is an example of a diagnostic likelihood ratio when "likely" is measured in odds. The likelihood ratio for a positive result is the post-test odds of disease divided by . . . [Full text of this article]


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