Module 38: A Simple Equation to Predict a Subscore’s Value

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Subscores are often used to indicate test-takers’ relative strengths and weaknesses and so help focus remediation. But a subscore is not worth reporting if it is too unreliable to believe or if it contains no information that is not already contained in the total score. It is possible, through the use of a simple linear equation provided in this note, to determine if a particular subscore adds enough value to be worth reporting.

Keywords:  added value, classical test theory, CTT, linear equation, subscores, reliability, orthogonal, proportional reduction in mean squared error, PRMSE

Richard A. Feinberg

National Board of Medical Examiners, Philadelphia, PA

Richard Feinberg is a Senior Psychometrician with NBME, where he leads and oversees the data analysis and score reporting activities for large-scale high-stakes licensure and credentialing examinations. He is also an Assistant Professor at the Philadelphia College of Osteopathic Medicine, Philadelphia, PA, where he teaches a course on Research Methods and Statistics.

His research interests include psychometric applications in the fields of educational and psychological testing.

He earned a PhD in Research Methodology and Evaluation from the University of Delaware, Newark, DE.

Howard Wainer


Howard Wainer is an American statistician, past principal research scientist at the Educational Testing Service, adjunct professor of statistics at the Wharton School of the University of Pennsylvania, and author, known for his contributions in the fields of statistics, psychometrics, and statistical graphics.


Module 38: A Simple Equation to Predict a Subscore’s Value
Open to download resource.
Open to download resource.