Retrospective diagnostic accuracy study

A retrospective diagnostic accuracy study evaluates how well a diagnostic test (the index test) correctly identifies a target condition by applying it to previously collected data or archived specimens alongside a reference standard. Because both index test results and reference standard results are drawn from existing records or stored material rather than generated prospectively, this design is faster and less costly than a prospective counterpart — but carries specific methodological risks that must be controlled to produce valid estimates of sensitivity, specificity, and related measures.