Why clinicians are natural bayesians: Bayesian confusion

doi:10.1136/bmj.330.7504.1390-a

BMJ 2005;330:1390 (11 June), doi:10.1136/bmj.330.7504.1390-a

Letter

Why clinicians are natural bayesians

Bayesian confusion

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

EDITOR—Gill et al say that the pretest odds multipliedby the likelihood ratio of a test provides the post test odds.¹However, Bayes's work referred to probability rather than odds.

Every part of clinical history andexamination can be seen as a diagnostic test

Credit: ROYALASIATIC SOCIETY/BAL

Bayes developed his famous theorem about conditional probability.He showed that the probability of some event A occurring giventhat event B has occurred is equal to the probability of eventB occurring given that event A has occurred, multiplied by theprobability of event A occurring and divided by the probabilityof event B occurring. Bayes theorem states: P(A|B) = P(A)x P(B|A)divided by P(B).

The fact that Bayes refers to probability and articles suchas those by Gill et al refer to odds has led to confusion, withsome people thinking that it does not make any . . . [Full text of this article]

David J R Hutchon, locum obstetrician and gynaecologist

Greymouth, New Zealand DJRHutchon@Postmaster.co.uk

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Why clinicians are natural bayesians: Christopher J Gill, Lora Sabin, and Christopher H Schmid
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