The psychometric properties of five scoring methods applied to the script concordance test

Purpose The Script Concordance Test (SCT) is designed to measure cognitive ability related to successful clinical decision making. An SCT's usefulness for medical education depends on establishing its construct validity. The SCT's present construct relates examinee's scores to experts' response patterns, which does not require a single-best-answer format. Because medical education assessments do require a single best answer, the authors compared the psychometric properties of two aggregate scoring methods with three single-best-answer scoring methods for an SCT. Method A nephrology SCT was developed and administered to 85 examinees. Examinees' scores derived from a key developed using eight experts and a traditional aggregate scoring method on a five-point Likert-based scale were compared with four alternate scoring methods (one method eliminated the multipoint Likert-type scale and three eliminated the Likert-type scale and employed single-best-answer scoring). Results Two of the four alternate scoring methods performed as well as the traditional Likert-type aggregate scoring method. Scores from all five methods were highly intercorrelated. in addition, each method produced scores similarly correlated with level of experience, and none exhibited an intermediate effect. Conclusions Single-best-answer scoring with three answer choices produced results similar to aggregate scoring on a Likert-type scale. Because SCT items appear to assess an examinee's understanding of the interrelatedness of medical knowledge, single-best-answer scoring on an SCT may be valid as an educational assessment. More research is needed to assess differential validity compared with multiple-choice question exams and the predictive validity related to clinical performance.