Determining the Minimally Clinically Important Difference for the Disability Rating Scale in Persons With Chronic Traumatic Brain Injury

Abstract

The Extended Glasgow Outcome Scale (GOSE) is accepted as the primary outcome measure in registrational studies for traumatic brain injury (TBI). The Disability Rating Scale (DRS) is used to assess functional progress from initial acute injury, through rehabilitation and reintegration into the community and life. For these reasons, the DRS is an alternative measure for assessing meaningful global outcomes in chronic TBI. The objective of this study was to determine the minimally clinically important difference (MCID) for the DRS in chronic TBI, by determining the magnitude of DRS change associated with the MCID for the GOSE of 1 point. This study is a retrospective analysis of the multi-center, prospective, longitudinal, Traumatic Brain Injury Model Systems National Database of persons with outcomes at 1, 2, and 5 years and every 5 years thereafter post-injury. Spearman's correlations for dynamic and static relationships between the DRS and GOSE were significant. For the 1-point MCID for the GOSE, the dynamic MCID estimate for the DRS of a −0.68-point change was calculated as the mean DRS change associated with the difference of the GOSE score between year 1 and year 2 (score range, 3–8), using all persons in the study (n = 11,102), whereas the exploratory static MCID estimate for the DRS of −1.28 points was calculated from the slope of the best-fit line between the DRS and GOSE at year 1 follow-up (score range, 3–8; n = 13,415). The final MCID for the DRS was calculated by using the triangulation method (i.e., the arithmetic mean of the dynamic and exploratory static MCID estimates), which resulted in a −1.0-point change. The significant correlation between the DRS and GOSE has allowed for the establishment of a −1.0-point MCID for the DRS, which supports the use of the DRS as an alternative primary outcome measure for chronic TBI research studies, including clinical trials.