Scales for rating psychotic and psychotic-like experiences as continua

Although psychotic symptoms are usually viewed as dichotomous events, both patients and nonpatients often report isolated psychotic experiences as well as psychotic-like experiences, the latter being attenuated versions of psychotic experiences. College students, previously identified as probably at high risk for psychosis, were interviewed using a modified Schedule for Affecting Disorders and Schizophrenia--Lifetime Version (SADS L). Eighty types of deviant experiences reported in the interviews fell into six categories: transmission of one's own thoughts, passivity experiences, thought withdrawal, voice and other auditory experiences, aberrant beliefs, and visual experiences. The 80 types of experience were rated on deviancy by six expert judges (coefficient alpha of raters = .94). The median ratings of the six judges were used to construct a manual. Two pairs of raters used the manual to rate excerpts of interview and obtained reliabilities of .78 and .81. This manual should be useful in evaluation of psychotic-like experiences, especially in studies of individuals believed to be at high risk for future development of clinical psychosis.