Biostats 2

probability of the disease before a test is done (basically the prevalence)

• based on outcome of the test, the likelihood that the
• patient has the disease (rule in/out)

ration or proportion of those with disease & test positive: without disease with positive test result (1-specificity)

Ration = those with disease & negative test result : without disease and negative test result (specificity)

• P - patient/population being addressed
• I - intervention in question
• C - comparison (when relevant)
• O - outcome of outcomes of interest

• Generate large and conclusive changes from pre-test and
• post-test probability.

Generate moderate shifts in pre-test to post-test probability.

Generate small (but sometimes important) shifts from pre- to post-test probability.

Alter probability to a small (a likely insignificant) degree

Formal structure integrating evidence (beneficial/harmful effects) with values, preference, probablilitys, costs associated

• Square- decision
• Circle - chance events
• Triangle - outcome nodes

When there are large changes between pre-test and post-test probability; validity compared to 'gold standard'

prevalenceof disease, sensitivity, specificity

• Contribution of test result as a single number
• Determining post -test probablilty given a result
• Summarizing information
• Describing probability of disease

Increase sensitivity

Increased sensitivity