Mary E. Kelley, Leonard White, Michael T. Compton, Philip D. Harvey

Although the items of the Positive and Negative Syndrome Scale (PANSS) are ordinal, continuous data methods are consistently used to analyze them. The current study addresses this issue by applying a categorical method and critically examining the ideas of item inclusion and goodness of fit. Data from 1527 subjects were used to test a proposed solution to the factor structure of the PANSS using a categorical factor analytic method. The model was made more generalizable by setting a minimum level of association between the item and the factor, and the results were then compared to existing solutions. The model was also tested for consistency in a first-episode sample. Use of categorical methods indicated similar results to previous analyses; however, it is demonstrated that the strength of the estimates can be unstable when items are shared across factors. The current study demonstrates that solutions can change substantially when a model is over-fitted, and therefore use of measures of fit as the criterion for an acceptable model can mask important relationships and decrease clinical validity.