COMBI >> Scales >> Overt Behaviour Scale >> Introduction


Glenn Kelly, PhD, Diverge Consulting Inc. at

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Kelly, G. (2010). The Overt Behaviour Scale. The Center for Outcome Measurement in Brain Injury.
combi/obs ( accessed ).





Introduction to the Overt Behaviour Scale

The Overt Behaviour Scale (OBS) was developed to record a range of challenging behaviours displayed by people with acquired brain injury (ABI) living in community settings. It incorporates the four modified verbal and physical aggression sub-scales of the Overt Aggression Scale[1] (i.e. Verbal aggression, Physical aggression against objects, Physical aggression against self, Physical aggression against other people) with five additional sub-scales: Inappropriate sexual behaviour, Perseveration/ repetition, Wandering/absconding, Inappropriate social behaviour, and Lack of initiation. Using these nine categories, the OBS presents 34 behavioural descriptors, each of which can be measured in terms of severity, frequency and impact. It has been shown to have good reliability, validity and responsiveness.

The OBS produces three key indices. The first, ‘Cluster’ (range 0–9), comprises the sum of the number of categories for which challenging behaviours have been observed. The second, ‘Total Levels’ (range 0–34), comprises the sum of the number of individual behaviour descriptors endorsed. The final score, ‘Total Clinical Weighted Severity (CWS)’ (range 0–84), reflects clinical opinion that some behaviours within each category are more severe than others.

The OBS provides clear operational definitions of behaviours of interest and a common language for frequently-encountered behaviours. It also provides an objective measure of behavioural severity, and its structured format helps to elicit information that might otherwise not be obtained because it promotes reporting of all challenging behaviours not only those most salient to an informant.

[1.] Yudofsky SM, Silver JM, Jackson W, Endicott J, Williams D. The Overt Aggression Scale for the objective rating of verbal and physical aggression. American Journal of Psychiatry, 1986; 143, 35–39.

The Overt Behaviour Scale was developed by the ABI Behaviour Consultancy, which was funded by the Victorian Department of Human Services under the auspice of Epworth Hospital, in partnership with the Brain Injury Rehabilitation Unit, Liverpool Hospital, Sydney Australia. Information regarding the OBS was contributed by Diverge Inc ( and Liverpool Brain Injury Rehabilitation Unit ( Please contact Glenn Kelly, Ph.D., at for more information.

If you find the information in the COMBI useful, please mention it when citing sources of information. The information on the OBS may be cited as:

Kelly, G. (2010). The Overt Behaviour Scale. The Center for Outcome Measurement in Brain Injury. ( accessed ).


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