Evidence-appraisal glossary
Index test
The diagnostic test whose accuracy is being evaluated in a study, measured by comparing its results against the reference standard.
Also called: test under evaluation.
In a diagnostic accuracy study the index test is the one under investigation, and its results are cross-tabulated against the reference standard to produce sensitivity, specificity, and predictive values. Reporting guidelines ask authors to describe exactly how the index test was performed and read, and whether its readers were blinded to the reference standard result. If the people interpreting the index test know the true diagnosis, the reported accuracy can be inflated.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.