Psychological assessment often requires concrete decisions, e.g. whether a person is “below the norm” in some psychological domain. It is still common that practitioners directly compare the test score with some theoretical norm value (e.g., one standard deviation below the mean). In a literature review, we show that all German textbooks on Psychological Assessment recommend taking measurement uncertainty of psychological tests into account, for example by using critical differences, hypothesis tests, or confidence intervals. However, these recommendations resemble heuristics without a comprehensible rationale on how to choose necessary parameters (e.g., the appropriate significance or confidence level). Statistical decision theory is a mathematical framework for making rational decisions. Although once en vogue in psychology (cf. Cronbach & Gleser, 1965), it receives little attention today. When viewed from a decision theoretic perspective, one can show the implicit assumptions of current decision heuristics. For example, using two-sided hypothesis tests and confidence intervals with significance level alpha = 0.05 implies that type I errors are 39 times as costly as type II errors. In this paper, we give a short introduction to decision theory and use this framework to discuss the implication of current assessment practices. We also present a small survey of clinical neuropsychologists, who reported different representations of their internal cost ratio for a fictitious assessment scenario. Although the practitioners’ cost ratios varied, the majority chose less extreme ratios than the common heuristics would imply. We argue that psychological assessment would benefit from explicitly considering decision theoretic implications in practice and outline possible future directions.

Sterner, P., Friemelt, B., Goretzko, D., Kraus, E. B., Bühner, M., & Pargent, F. (2022, June 10). The confidence/significance level implies a certain cost ratio between type I error and type II error: For a stronger focus on decision theory in psychological assessment – Das Konfidenz-/Signifikanzniveau impliziert ein bestimmtes Kostenverhältnis zwischen Fehler 1. Art und Fehler 2. Art: Für ein stärkeres Einbeziehen der Entscheidungstheorie in die psychologische Einzelfalldiagnostik. https://doi.org/10.31234/osf.io/rsqvt