Objective To evaluate the ability of case vignettes to assess the performance of symptom checker applications and to suggest refinements of the methods of case vignette-based audit studies.

Methods We re-analyzed the publicly available data of two prominent case vignette-based symptom checker audit studies by calculating common metrics of test theory. Furthermore, we developed a new metric, the Capability Comparison Score (CCS), which controls for different degrees of item difficulty of the set of cases each symptom checker evaluated. We then scrutinized whether applying test theory and the CCS alter the performance ranking of the investigated symptom checkers.

Results In both studies most symptom checkers changed their rank order of triage capability when adjusting for item difficulty with the CCS. The previously reported triage accuracies commonly overestimated the capability of symptom checkers because they do not account for the fact that symptom checkers tend to selectively appraise easier cases. Many case vignettes in both studies showed insufficient (very low and even negative) values of item-total correlation.

Conclusions A test theoretic perspective helps identify previously unreported limitations to the validity of case vignette-based symptom checker assessments and provides guidance on how to improve the quality of case vignettes and metrics for appraising their quality. A more elaborate metric, which accounts for item difficulty of vignettes an app did (not) evaluate, might prove more meaningful than accuracy alone for competitive assessment of symptom checkers. Our approach contributes to standardizing the methods to appraise symptom checker capability to yield more generalizable results.

The authors have declared no competing interest.

The authors received no specific funding for this work.

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Since we did not collect data but used data collected from other authors, we do not publish the dataset used. Generated data can be found in the Appendix.