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Agitated Behavior Scale Properties
Normative Data
The means and standard deviations for the Total Score and subscale scores are based on samples of persons with traumatic brain injury treated during the acute phases of recovery on an inpatient, rehabilitation unit. A prospective sample of all patients with brain injuries, regardless whether they were demonstrating agitation, revealed an overall mean ABS score of 21.01 and standard deviation of 7.35 for day shift nursing observations (Corrigan, 1989). For clinical purposes, we consider any scores (Total or converted subscale) 21 or below to be within normal limits; from 22 through 28 to indicate mild occurrence; 29 through 35 to indicate moderate; and more than 35 to be severe.
While norms based on a broader sampling of patients from other institutions will be desirable, the ABS remains quite usable for ipsative comparisons of the same individual from shift to shift, therapy to therapy, and/or day to day. A sample of the graphic presentation of data used on the Traumatic Brain Injury Unit at Ohio State University is attached to this summary.
Reliability
The initial validation studies (Corrigan, 1989) showed correlations between ratings conducted on the same day exceeded .70 for the Total score (subscale scores were not available at that time). Inter-rater reliability was recently re-examined (Bogner, Corrigan, Stange, & Rabold, 1999) due to the instrument’s increased use with different populations, rated by individuals from various disciplines, based on a variety of observation periods.
With a sample of persons receiving acute rehabilitation for acquired brain
injury, research assistants (psychology interns and a rehabilitation nurse)
rated behavior based on 10-minute observation periods. The research assistants’
ratings yielded a correlation coefficient for the Total score of .92.
Comparable correlation coefficients were obtained for the factors Disinhibition,
Aggression, however the correlation coefficient for Lability was lower,
likely due to the small number of items used in its calculation.
Inter-rater reliability was also examined with a sample of individuals
residing in a long-term care facility whose primary diagnosis was dementia.
The ratings were again made by research assistants based on 10-minute
observation periods. The correlation coefficient for the Total score was
.91, while the coefficients for the factor scores were in the high .80s.
Examination of the internal consistency of the scale found Cronbach's alphas ranging from .83 to .92 in the original validation study (Corrigan, 1989). With the two samples examined by Bogner et al (1999), Cronbach’s alphas ranged from .74 to .92. The relatively high internal consistency of the scale suggests that agitation, as measured by the ABS, is a unitary construct, with three facets being individually prominent at times.
Validity
The original development of the ABS demonstrated the content validity of items and concurrent validity of the Total Score. Subsequent studies have shown the ABS to be predictive of change in cognitive status (Corrigan & Mysiw, 1988) and able to differentiate confusion and inattention (Corrigan & Mysiw, 1988; Corrigan et al., 1992).
Subsequent studies have provided support for the construct validity of
the ABS (Corrigan & Mysiw, 1988; Corrigan, Mysiw, Gribble & Chock,
1992; Corrigan, Bogner, & Tabloski, 1996; Novack & Penrod, 1993;
Tabloski, McKinnon-Howe, & Remington, 1995). Both factor analysis
as well as Rasch analysis have indicated that agitation is best represented
as one general construct with three underlying, correlated factors: Aggression,
Disinhibition, and Lability (Corrigan and Bogner, 1994; Bogner, Corrigan,
Bode & Heinemann, 2000). The Total Score remains the best measure
of agitation, but subscale scores may provide important additional clinical
and research data.