# Pre and post test odds

## Pre-test odds

The odds that the patient has the target disorder before the test is carried out (pre-test probability/[1 – pre-test probability]).

## Post-test odds

The odds that the patient has the target disorder after the test is carried out (pre-test odds x likelihood ratio).

# Pre and post test probability

## Pre-test probability

The proportion of people with the target disorder in the population at risk at a specific time (point prevalence) or time interval (period prevalence). Prevalence may depend on how a disorder is diagnosed. A good example is dementia.

## Post-test probability

The proportion of patients with that particular test result who have the target disorder (post test odds/[1 + post-test odds]).