Scalability of the Positive and Negative Syndrome Scale in first‐episode schizophrenia assessed by Rasch models

Abstract

Objective Historically, assessment of the psychometric properties of the Positive and Negative Syndrome Scale (PANSS) has had several foci: (1) calculation of reliability indexes, (2) extraction of subdimensions from the scale, and (3) assessment of the validity of the total score. In this study, we aimed to examine the scalability and to assess the clinical performance of the 30‐item PANSS total score as well as the scalability of a shorter version (PANSS‐6) of the scale. Methods A composite data set of 1073 patients with first‐episode schizophrenia or schizophrenia spectrum disorder was subjected to Rasch analysis of PANSS data from baseline and 4–6 weeks follow‐up. Results The central tests of fit of the Rasch model failed to satisfy the statistical requirements behind item homogeneity for the PANSS‐30 as well as the PANSS‐6 total score. For the PANSS‐30, Differential Item Functioning was pronounced both for the 7‐point Likert scale rating categories and when dichotomizing the rating categories. Subsequently, the Rasch structure analysis in the context of dichotomized items was used to isolate and estimate a systematic error because of item inhomogeneity, as well as a random error. The size of the combined sources of error for the PANSS‐30 total score approximated 20% which is often regarded as clinical cut‐off between response versus no‐response. Conclusion The results demonstrate the operational consequences of a lack of statistical fit of the Rasch model and suggest that the calculated measure of uncertainty needs to be considered when using the PANSS‐30 total score.

Exploratory rasch analysis of a static-99R clinical cohort assessment

“…One method within modern test theory is Rasch analysis [ 14 ], which is part of the Item Response Theory (IRT) family of statistical methods. While originally developed for quantifying problem-solving ability in the school environment, Rasch analysis has also been applied to several scales used in clinical psychiatry [ 15 – 21 ] and forensic contexts [ 22 – 24 ]. The construct validity of the Static-99 and its revised version, the Static-99R, has been examined in previous studies using factor analysis [ 25 , 26 ] and a non-parametric IRT procedure [ 27 ] on non-clinical samples.…”

Scalability of the positive and negative syndrome scale: The role of diagnostic heterogeneity and inter‐rater reliability

“…Dear Editor, We read the recent article by Baandrup et al 1 with interest. Baandrup et al have analyzed data from three clinical studies and conclude that neither the full Positive and Negative Syndrome Scale (PANSS) 2 nor the 6-item subscale of the PANSS (PANSS-6) is scalable according to Rasch models.…”

“…In fact, the mixture imbedded in data may secure a spread of patient severity levels which will not be met by representative sampling in one population." 1 Based on the potential effect of diagnostic heterogeneity outlined above, we consider this interpretation to be questionable.…”