Background: This study aimed to establish the minimal clinically important difference (MCID) for the Fugl-Meyer Motor Scale (FMMS) and the Disability Rating Scale (DRS) to evaluate interventions in patients with motor deficits in the chronic phase after traumatic brain injury (TBI). Methods: MCIDs were established with a structured expert consultation process, the RAND/UCLA modified Delphi method. This process consisted of a literature review and input from a 10-person, multidisciplinary expert panel. The experts were asked to rate meaningfulness of improvements in hypothetical patients and numeric changes via two rounds of ratings and an in-person meeting. Results: The estimated MCIDs were six and five points on the FMMS Upper and Lower Extremity Scale, respectively, and one point on the DRS. The experts argued against establishing an MCID for the combined FMMS because the same change was more likely to be meaningful if concentrated in one extremity and because a meaningful improvement in one extremity implies meaningfulness irrespective of the changes in the other. Conclusions: This study is the first to establish MCIDs for the FMMS and the DRS in the chronic phase after TBI. The results may be helpful for the design and interpretation of clinical trials of interventions.
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