COMBI >> Scales >> Overt Behaviour Scale >> Syllabus


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 ).





OBS Syllabus


Administration guidelines are detailed in a separate document available on this site. Please see OBS Guidelines. A brief overview is provided here.

The OBS was designed for use in a semi-structured interview in which an ABI-knowledgeable clinician interviews one or more informants who knows the client well. For each of 34 behavioural descriptors, a rater determines from the informant whether that behaviour has occurred in the time period specified (one month or three months is typically used). Only descriptors that have occurred need scoring. First, by ticking a box showing that a behaviour occurred, the severity of the behaviour is also recorded because items are arranged in a predetermined order of severity. The behaviour’s frequency is then scored using a number from 1 to 5 with the following definitions: 1 = less often than once per month, 2 = once a month or more, 3 = once a week or more, 4 = once a day, 5 = multiple times each day. The impact of the behaviour is then scored. “Impact” refers to the amount of emotional distress and/or practical disruption that a challenging behaviour causes. For example, impact refers to one’s experience of stress, worry, concern, or fear as a result of the behaviour. But impact can also refer to practical difficulties including the need for additional staff, altered procedures, dealing with complaints from families or other residents, or having to acquire additional supports such as psychiatrists, police, or behaviour intervention. Disruption often translates into additional costs. Informants are asked to score how much a behaviour impacts upon themselves and/or other people by using a number from 1 to 5 and the following definitions: 1 = no impact, 2 = minor impact, 3 = moderate impact, 4 = severe impact, 5 = extremely severe impact.

One of the 9 behavioural categories (Lack of Initiation, INI) is qualitatively different to the other categories because it involves an absence of overt behaviours. Experience in trialling a number of pilot versions of this subscale found difficulties in creating a multi-level version. As a result, INI was treated as a dichotomous sub-scale (present vs. absent). Some scoring adjustments are required to reflect this, and severity is indicated by the level of prompting required throughout a day (range: 1 = less than once/day, 5 = all tasks, everyday).


Clear scoring instructions and a scoring template are provided on the last page of the OBS.

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 severity levels 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.

Scores on the OBS can be compared to those obtained by an Australian sample of 190 clients referred to a specialist tertiary ABI-behaviour management service (that is, a sample in which having challenging behaviour is an inclusion criteria) (see Kelly et al., 2008)


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