COMBI >> Scales >> DRS >> Properties


Ms. Sarah Lavoie
Clinical Support Program Coordinator
Santa Clara Valley Medical Center

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Wright, J. (2000). The Disability Rating Scale. The Center for Outcome Measurement in Brain Injury.
combi/drs ( accessed ).*

*Note: This citation is for the COMBI web material. Mr. Wright is not the scale author for the DRS.






DRS Properties

Reliability of the DRS

Inter-rater reliability of the DRS was established among three raters on a sample of 88 TBI rehabilitation inpatients (Rappaport et al., 1982). Pearson correlations were .97-.98. In a separate study by Gouvier (1987), Spearman rho correlation coefficients were .98 among three raters on a sample of 37-45 subjects.

Novack et al. (1991) reported inter-rater reliability in a study of 27 severely brain injured persons. A comparison of DRS ratings by family members vs. rehabilitation professionals yielded significant correlations for both rehabilitation admission (r=.95) and discharge (r=.93) ratings.

Test-retest reliability was demonstrated by Gouvier (1987) in which a Spearman rho correlation of .95 was reported.


Validity of the DRS

Concurrent Validity was established in the initial publication on the DRS (Rappaport et al., 1982), in which abnormality ratings of the auditory, visual and somatosensory brain evoked potentials were significantly correlated with DRS ratings (r=.35 to .78). Additional validation of the scale is documented in a published article by K. Hall and co-workers (1993).

A correlation of DRS with simultaneously obtained GOS scores at two time intervals was demonstrated in a sample of 70 TBI inpatients (r=.50 at admission and .67 at discharge; Hall et al., 1985). Gouvier found a Spearman rho correlation of .92 between the rehabilitation admission DRS and the Stover Zeiger Scale (1976). The rehabilitation discharge DRS was correlated .81 with the discharge S-Z, .80 with the GOS (1975, 1981), and .85 with the Expanded GOS (Smith 1979).


Predictive validity

DRS scores obtained on 128 individuals within 72 hours of CVA or TBI were significantly correlated with acute hospital length of stay, DRS scores at discharge, and disposition at discharge (r=.50, .66 and .40 respectively; Eliason and Topp, 1984). Predictive validity of the DRS at admission was also demonstrated by Gouvier (1987). The correlation with the discharge S-Z was .65, and with the Expanded Glasgow Outcome Scale (Smith and Fields, 1979), r=.73. Initial DRS scores correlated significantly (r=.53, p<.01, n=77) with DRS one year later (Rappaport, 1982). Fryer and Haffey (1987) reported the DRS at admission to a cognitive rehabilitation program as a strong predictor of disability at follow up (r=.77, p< .001). It also discriminated between those outpatients who received Cognitive Rehabilitation/Community Readaptation training vs. those who did not.


The Ability of the DRS to Predict Employment

The DRS has been used to predict employment after TBI. Novack et al. (1988) stated that "the DRS documents recovery from disability and may help in predicting outcome, particularly for the more severely injured." His study found that DRS scores >15 on rehabilitation admission, >7 on discharge, and >4 at three months were incompatible with return to work one to two years post injury.

In a sample of 145 TBI clients, Cope et al. (1991) reported a differential return to competitive employment or school based on rehabilitation admission DRS scores. One year post-discharge from a post-acute rehabilitation system, 62% of those with an admission DRS of 1-3 (mild) were employed competitively or in school. In the group with an admission score of 4-6 (Moderate), 39% were employed or in school one year later. Those with a DRS of 7-20 (severe) had an 11% employment/school rate one year later. That is, only 6 of the 54 clients falling in the severe range on admission were working competitively or in school one year later.

In a sample of 55 cases of TBI (average DRS of 13.3 (severe) at rehabilitation admission and 5.7 (moderate) at follow-up, Rappaport et al. (1989) found that 9% were employed full-time five to ten years after their injury. Additionally, none of the individuals who previously held professional positions were able to return to them after the injury, and none of the other TBI individuals were able to attain professional positions. Eighty-seven percent of these people were dependent on society to provide financial support for the basic fundamentals of food, clothing, and shelter. None of these individuals was dependent before injury.

Rao and Kilgore (1990) found that the rehabilitation admission and discharge DRS scores combined predicted return to work with 76% accuracy in a sample of 57 individuals with TBI. In a later study, Rao and Kilgore (1992) found no significant difference between the DRS and other good predictors of return to work/school. When they considered a history of substance abuse as a negative indicator, the DRS (admission+discharge scores) predicted correctly 17 of 19 cases as unable to return to work 14 to 26 months after injury.


Rasch Analysis (Hall et al., 1993)

Rasch analysis was completed on the eight DRS item scores at rehabilitation admission for 266 cases. Composite scores of 1 to 29 were obtained (0 is normal, 30 is dead: clients who were rated "normal" were omitted). The findings were:

  • The relative level of difficulty between admission and discharge ratings of the DRS items for 256 cases was consistent.
  • The range of difficulty reflected in the scale is excellent, from items measuring very simple functioning to those measuring complex functions.
  • The level of difficulty of the items is as follows: Eye Opening, Communication Ability, Motor Response, Feeding, Toileting, Grooming, Level of Functioning, and Employability.
  • The difficulty level of the three items "Cognitive Ability for Feeding, Toileting, and Grooming" were very similar.
  • There is a "gap" between "Cognitive Ability for Feeding, Toileting and Grooming" and "Level of Functioning" (i.e. ability to live independently) and between the latter and "Employability." The functional difficulty of each of these items is substantially different, with no intervening items to reflect intermediate abilities. This is consistent with the observation of less sensitivity to change in the DRS in individuals at high functional levels.

In summary, the Rasch analysis provided transformed scores for use in interval scale data analyses and validated the observations about the DRS: a scale that measures a wide range of disability with less sensitivity at the high end (mild TBI). Items discriminate well the varying levels of disability and relative difficulty of items remains constant between admission and discharge.

In the analysis of the TBI Model Systems National Database data, the average DRS untransformed score at rehabilitation admission was 12 (rounded), at discharge, 5, and at one year post injury follow up, 3, in a sample of 70 cases with complete data at all three time intervals.


Ceiling Effects (Hall et al., 1996)

The average DRS scores at rehabilitation admission, discharge, one year and two years post injury for all cases with data in the TBI Model Systems database were analyzed for ceiling and floor effects.

Ceiling is defined as mean score of 0, 1 or 2 on the DRS (top 10% of scale). These "ceiling" scores define independent or modified independent status. The DRS has virtually no ceiling effect at discharge, year 1 and year 2 after injury on a consistent sample over time. Results including all cases with data available at any time period were similar, with sample sizes ranging from 598 to 206.

The DRS was developed with the continuum of recovery in mind. The DRS consistently demonstrates good scale properties and has been shown to predict employment well. At one year post injury, twenty-nine percent of the FIM and FIM+FAM scale reflects independence/modified independence (scores of 6 and 7 on a 7 point scale) and only 10% of the DRS summed score represents this level of independence (scores of 0,1 and 2 on a 30 point scale). This difference gives the DRS an advantage in regard to ceiling effect.


Use of .5 ratings:

In 1994, the Traumatic Brain Injury Model Systems (TBIMS) National Database adopted a 0.5 rating option for the last 5 items of the DRS. Although raters found the half point discrimination useful, no validation study was ever completed on the use of the 0.5 rating option. In 2010, the TBIMS National Database members voted to omit the 0.5 rating option. Use of the 0.5 rating option after April 1, 2010 is not recommended.


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