Evaluating bizarre-idiosyncratic thinking: a comprehensive index of positive thought disorder.

A summary of our method of assessing positive thought disorder, or bizarre-idiosyncratic thinking, from two short verbal tests is presented. This measure provides for standardized thought disorder assessments of: the overall presence and severity of thought disorder, and the type of disordered thinking shown. A definition and examples of bizarre-idiosyncratic thinking are provided, along with information on the reliability and validity of the scoring system. A method of establishing subject groups based on the severity of positive thought disorder also is presented--ranging from no thought disorder, to abnormal thinking, to severe formal thought disorder. This measure has been used to assess longitudinal changes in thought disorder symptoms over time and to evaluate relationships between thought disorder, other aspects of psychopathology (such as delusions), and adjustment in other areas of functioning across diagnostic groups.