Objective Few previous studies evaluating the benefits of diagnostic decision support systems have simultaneously measured changes in diagnostic quality and clinical management prompted by use of the system. This paper describes a reliable and valid scoring technique to measure the quality of clinical decision plans in an acute medical setting, where diagnostic decision support tools might prove most useful.

Design Sets of differential diagnoses and clinical management plans generated by 71 clinicians for 6 simulated cases, before and after decision-support from a Web-based paediatric differential diagnostic tool (ISABEL), were used.

Measurements A composite quality score was calculated separately for each diagnostic and management plan by considering the appropriateness value of each component diagnostic or management suggestion, a weighted sum of individual suggestion ratings, relevance of the entire plan and its comprehensiveness. The reliability and validity (face, concurrent, construct and content) of these two final scores were examined.

Results 252 diagnostic and 350 management suggestions were included in the inter-rater reliability analysis. There was good agreement between raters (intraclass correlation coefficient 0.79 for diagnoses, and 0.72 for management). No counterintuitive scores were demonstrated on visual inspection of the sets. Content validity was verified by a consultation process with paediatricians. Both scores discriminated adequately between the plans of consultants and medical students, and correlated well with clinicians' subjective opinion of overall plan quality (Spearman 0.65, p<0.01). The diagnostic and management scores for each episode showed moderate correlation (r=0.51).

Conclusion The scores described can be used as key outcome measures in a larger study to fully assess the value of diagnostic decision aids, such as the ISABEL system.