From mandating common measures to mandating common metrics: a plea to harmonize measurement results

Objective. There is a great variety of measurement instruments to assess similar constructs in experimental psychological research and clinical practice. This complicates the interpretation of measurement results and hampers the implementation of measurement-based care. Actions have been proposed to improve matters, such as mandating a limited set of outcome measures as a prerequisite to obtain research funding. Method. We propagate an alternative or supplementary strategy: converting test results into universally applicable common metrics. Results. Two metrics are reviewed: T scores and percentile ranks. Their calculation is explained, and their merits and shortcomings discussed using data from three common measures for depression, the CES-D, PHQ-9, and BDI-II. Conclusion. We conclude with a proposal to express test results as T scores with the general population as reference group and supplement these with percentile ranks based on data from clinical and population samples.