Assessment of Symptoms in Schizophrenia

The Schizophrenia Bulletin (1983, 9(3):368-376) carries an article by RRJ Lewine, L Fogg and HY Meltzer (University of Chicago Pritzker School of Medicine and Illinois State Psychiatric Institute) entitled "Assessment of negative and positive symptoms in schizophrenia." The authors introduce the concept of sample- and instrument-free additive measurement and apply this concept to the "Schedule for Affective Disorders and Schizophrenia-Current" (SADS-C) and the "Nurses' Observation Scale for Inpatient Evaluation" (NOSIE). Their study addresses problems in the theoretical and practical meaning of negative and positive symptoms in schizophrenia; the general conclusion is that a uni-dimensional scale for the measurement of negative symptoms is probably within reach, provided that more research concerning construct validity is completed.

A 1986 comment on this article by B Grau (University of Illinois at Chicago) and KT Mueser (Eastern Pennsylvania Psychiatric Institute) appears in the same journal (12(1):7-8). These authors point out that the negative symptom scales produced by the SADS-C and the NOSIE do not correlate, possibly for reasons of differing item content or methods of data collection cited by Lewine, Fogg and Meltzer. Grau and Mueser go on to say that the multi-dimensionality of the data requires that "the Rasch model should accordingly be rejected for the domain of negative symptoms as a whole".

Lewine responds to Grau and Mueser in the same issue of Schizophrenia Bulletin (pp. 9-11), pointing out that their rejection of Rasch's approach to measurement ignores the difficulties and opportunities that attend the conceptual and methodological transition from educational data to psychiatric data. In fact substantive differences in content and method between the SADS-C and NOSIE are so great as to lead one to wonder how they could ever have been held to measure the same thing. Lewine points out that, although Grau and Mueser come upon it for the wrong reasons, their question concerning the uni- dimensionality of the negative symptoms construct is important, interesting and legitimate.

This interchange brings out a basic problem. If the definition of objective measurement implemented by Rasch's approach is rejected, how can anyone assess multi-dimensional constructs since they then remain fundamentally and inextricably confounded with one another? By undertaking quantitative research in a careful and thoughtful manner, Lewine has taken basic steps toward the implementation of fundamental measurement in the setting of schizophrenic symptoms.

Assessment of Symptoms in Schizophrenia, W Fisher Jr. … Rasch Measurement Transactions, 1990, 4:3 p. 113

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Rating Scale Analysis, Wright & Masters Introduction to Rasch Measurement, E. Smith & R. Smith Introduction to Many-Facet Rasch Measurement, Thomas Eckes Invariant Measurement: Using Rasch Models in the Social, Behavioral, and Health Sciences, George Engelhard, Jr. Statistical Analyses for Language Testers, Rita Green
Rasch Models: Foundations, Recent Developments, and Applications, Fischer & Molenaar Journal of Applied Measurement Rasch models for measurement, David Andrich Constructing Measures, Mark Wilson Rasch Analysis in the Human Sciences, Boone, Stave, Yale
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