(bāz )
[Thomas Bayes, Brit. mathematician, 1702-1761]
A statistical theorem concerned with analyzing the probability that a patient may have a specific condition after diagnostic testing. The theorem states that if a disease is very rare (the pretest probability is low), the patient is unlikely to have that condition even with a positive diagnostic test. Conversely, when the pretest probability of a specific condition is very high, a negative test result does not rule out the condition.