The correct denominator
The calculation starts with positive results: true positives divided by all positives. It answers a question about a positive result in that population, whereas sensitivity starts with people who have the condition.
Why it changes across settings
Condition frequency in the assessed population influences predictive value. The same sensitivity and specificity can therefore accompany different predictive values in different populations. Participant selection and result verification also matter.
Applying a table
When using a 2×2 tool, identify the condition, reference standard and origin of the counts. Communicate population and uncertainty. A study estimate must not be presented as a certain individual probability.
Interpretation limits
Positive predictive value is not a fixed test property across all populations.
Original references
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Research questions
Select tools by method, population and purpose. A thematic connection does not validate use in every case.
Educational content for framing research. Consult the original document, study population and methodology before interpreting a conclusion. Methodology