A Rasch analysis of three of the Wisconsin Scales of Psychosis Proneness: measurement of schizotypy.

Rasch analyses were conducted with data from 90 university students on three of the Wisconsin Scales of Psychosis Proneness--the Magical Ideation (Eckblad & Chapman, 1983), Perceptual Aberration (Chapman, Chapman, & Raulin, 1978), and Revised Social Anhedonia Scales (Eckblad, Chapman, Chapman, & Mishlove, 1982). All of the items for each of the individual scales, plus all of the items from the combined Perceptual Aberration/Magical Ideation (Per-Mag) Scale, showed satisfactory fit to the Rasch model. These results show that personality traits including these psychosis proneness, or schizotypy, traits can be measured on a theoretically sound quantitative interval scale. Rasch scale equivalents for raw scores are provided. Possible improvements to the Magical Ideation, Perceptual Aberration, and Per-Mag scales are suggested by the item analysis. Advantages of Rasch scaling for clinical applications include detection of invalid test protocols, more meaningful interpretations of test scores, and direct comparison of scores from different tests of the same construct.