Use of NON-PARAMETRIC Item Response Theory to develop a shortened version of the Positive and Negative Syndrome Scale (PANSS)

doi:10.1186/1471-244X-11-178

BMC Psychiatry. 2011; 11: 178.

Published online 2011 November 16. doi: 10.1186/1471-244X-11-178

PMCID: PMC3256111

Use of NON-PARAMETRIC Item Response Theory to develop a shortened version of the Positive and Negative Syndrome Scale (PANSS)

Anzalee Khan,^1,^2,⁴ Charles Lewis,^#^1,⁶ and Jean-Pierre Lindenmayer^#^3,^4,⁵

¹Fordham University, Department of Psychometrics, Bronx, NY, USA

²ProPhase, LLC, New York, NY, USA

³New York University, School of Medicine, New York, NY, USA

⁴Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, USA

⁵Manhattan Psychiatric Center, Wards Island, NY, USA

⁶Educational Testing Services, ETS, Princeton, NJ, USA

Corresponding author.

^#Contributed equally.

Anzalee Khan: akhan/at/nki.rfmh.org; Charles Lewis: clewis/at/fordham.edu; Jean-Pierre Lindenmayer: lindenmayer/at/nki.rfmh.org

Received March 14, 2011; Accepted November 16, 2011.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Nonparametric item response theory (IRT) was used to examine (a) the performance of the 30 Positive and Negative Syndrome Scale (PANSS) items and their options ((levels of severity), (b) the effectiveness of various subscales to discriminate among differences in symptom severity, and (c) the development of an abbreviated PANSS (Mini-PANSS) based on IRT and a method to link scores to the original PANSS.

Methods

Baseline PANSS scores from 7,187 patients with Schizophrenia or Schizoaffective disorder who were enrolled between 1995 and 2005 in psychopharmacology trials were obtained. Option characteristic curves (OCCs) and Item Characteristic Curves (ICCs) were constructed to examine the probability of rating each of seven options within each of 30 PANSS items as a function of subscale severity, and summed-score linking was applied to items selected for the Mini-PANSS.

Results

The majority of items forming the Positive and Negative subscales (i.e. 19 items) performed very well and discriminate better along symptom severity compared to the General Psychopathology subscale. Six of the seven Positive Symptom items, six of the seven Negative Symptom items, and seven out of the 16 General Psychopathology items were retained for inclusion in the Mini-PANSS. Summed score linking and linear interpolation was able to produce a translation table for comparing total subscale scores of the Mini-PANSS to total subscale scores on the original PANSS. Results show scores on the subscales of the Mini-PANSS can be linked to scores on the original PANSS subscales, with very little bias.

Conclusions

The study demonstrated the utility of non-parametric IRT in examining the item properties of the PANSS and to allow selection of items for an abbreviated PANSS scale. The comparisons between the 30-item PANSS and the Mini-PANSS revealed that the shorter version is comparable to the 30-item PANSS, but when applying IRT, the Mini-PANSS is also a good indicator of illness severity.

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