Children's Global Assessment Scale (CGAS) in a naturalistic clinical setting: Inter-rater reliability and comparison with expert ratings

The Children's Global Assessment Scale (CGAS) is a tool to assess the overall level of functioning of children in Child and Adolescent Mental Health Services (CAMHS). Even though the use of this rating scale requires trained raters, it is commonly deployed without prior training in clinical settings. The aim of this study was to investigate the reliability and the agreement of CGAS ratings with an expert rating, in a clinical setting with untrained raters. Five experienced clinicians rated five vignettes to provide expert ratings. These vignettes were then rated by 703 health-care professionals representing 33 Swedish CAMHS. The health-care professionals rated the vignettes significantly higher (showing better global functioning) than the expert ratings. There was a wide range between the minimum and maximum ratings. The intraclass correlation coefficient was 0.73, which indicates moderate inter-rater reliability. Neither clinical experience nor earlier experience of using CGAS influenced the agreement with the expert ratings. The inter-rater reliability is moderate when CGAS is used in a clinical setting with untrained raters. Further, the untrained raters differed substantially from the experts. This stresses the importance of proper training in conjunction with the introduction of new rating scales.