The longitudinal use of the Global Assessment Scale in multiple-rater situations.

The Global Assessment Scale was used by multiple clinicians to rate 108 chronically mentally ill outpatients for 18 months. With prior training, high interrater reliability was obtained. Analysis suggests that fluctuations in patients' scores were not attributable to measurement error due to the sequential ratings of multiple clinicians. Moreover, GAS means were inversely correlated with decompensations over the study period. Results indicate that the DMS-III-R recommended use of the GAS in multiple-rater outpatient facilities can be both reliable and clinically useful when supported by thorough staff training.