German version, inter- and intrarater reliability and internal consistency of the "Agitated Behavior Scale" (ABS-G) in patients with moderate to severe traumatic brain injury

Background: Agitation is frequently observed during early recovery after traumatic brain injury (TBI). Agitated behaviour often interferes with a goal-orientated rehabilitation and can be a substantial hindrance to therapy. Despite the relatively high occurance of agitation in TBI population there is no objective assessement in German (G) available. An existing scale with excellent psychometric properties is the "Agitated Behavior Scale (ABS)" developed by Corrigan in 1989. The aim of the study was to translate the Agitated Behavior Scale (ABS) into German (ABS-G) and investigate the inter-and intrarater reliability and internal consistency in patients with moderate to severe TBI. Methods: A formal nine-step translation and cross-cultural adaptation procedure (TCCA) was applied. Subsequently a prospective observational patient study was conducted. To examine the interrater reliability and internal consistency, two therapists rated 20 patients independently after a therapy session. This procedure was repeated twice on a weekly basis. The intrarater reliability was assessed through video recordings from three patients. Nine raters scored the demonstrated behaviour on the videotape with the ABS-G independently twice within one month. The inter-and intrarater reliability were evaluated with the Spearman rank correlation coefficient and the quadratic weighted kappa. The internal consistency was tested with Cronbach's alpha. Results: Behaviour of 20 patients (18 males; mean age 41 +/- 20.7; mean Functional Independence Measure (FIM) cognitive score on admission 7.1 +/- 4.04; mean ABS-G score at first observation 17.3 +/- 2.83) was assessed threefold. Interrater reliability yielded a correlation coefficient for ABS-G total score of all 60 paired observations of r(s) 0.845 and a weighted Kappa of 0.738. Intrarater reliability for ABS-G total score ranged between rs 0.719 and 0.953 and showed a weighted Kappa between 0.871 and 0.953. Cronbach's alpha indicated moderate internal consistency with 0.661. Conclusion: This study demonstrates that the ABS-G is a reliable instrument for evaluating agitation in patients with moderate to severe TBI. Hereby it would be possible to monitor agitation objectively and optimise the management of agitated patients according to international recommendations.