Objective
The 30-item Positive and Negative Syndrome Scale (PANSS-30) is the most widely used rating scale in schizophrenia, but too long for clinical use. Shorter PANSS versions have been proposed, including the PANSS-14 and PANSS-8. However, none of these PANSS versions has been validated using the parametric Rasch rating scale model, which evaluates ‘scalability’. Scalability means that each item in a rating scale provides unique information regarding syndrome severity and is a statistical prerequisite for using the total score as a measure of overall severity.

Method
Based on data from two randomized placebo-controlled trials in schizophrenia, we tested the scalability of PANSS-30, PANSS-14 and PANSS-8 by means of the parametric Rasch rating scale model. Furthermore, we tested whether a scalable PANSS version could separate efficacy of haloperidol and sertindole from placebo.

Results
Neither PANSS-30, PANSS-14 nor PANSS-8 was scalable. However, PANSS-6, consisting of the items: P1-Delusions, P2-Conceptual disorganization, P3-Hallucinations, N1-Blunted Affect, N4-Social withdrawal, N6-Lack of spontaneity and flow of conversation, was scalable. Furthermore, PANSS-6 captured superior symptom reduction and higher remission rates during treatment with haloperidol and sertindole vs. placebo.

Conclusion
PANSS-6 is a short schizophrenia severity rating scale that adequately separates antipsychotic efficacy from that of placebo.