Evidence for the validity of the modified dynamic gait index across diagnostic groups.

BACKGROUND: The modified Dynamic Gait Index (mDGI) measures the capacity to adapt gait to complex tasks utilizing 8 tasks and 3 facets of performance. The measurement stability of the mDGI in specific diagnostic groups is unknown. OBJECTIVE: This study examined the psychometric properties of the mDGI in 5 diagnostic groups. DESIGN: This was a cross-sectional, descriptive study. METHODS: A total of 794 participants were included in the study: 140 controls, 239 with stroke, 140 with vestibular dysfunction, 100 with traumatic brain injury, 91 with gait abnormality, and 84 with Parkinson disease. Differential item functioning analysis was used to examine the comparability of scores across diagnoses. Internal consistency was computed using Cronbach alpha. Factor analysis was used to examine the factor loadings for the 3 performance facet scores. Minimal detectable change at the 95% confidence level (MDC95%) was calculated for each of the groups. RESULTS: Less than 5% of comparisons demonstrated moderate to large differential item functioning, suggesting that item scores had the same order of difficulty for individuals in all 5 diagnostic groups. For all 5 patient groups, 3 factors had eigenvalues >1.0 and explained 80% of the variability in scores, supporting the importance of characterizing mobility performance with respect to time, level of assistance, and gait pattern. LIMITATIONS: There were uneven sample sizes in the 6 groups. CONCLUSIONS: The strength of the psychometric properties of the mDGI across the 5 diagnostic groups further supports the validity and usefulness of scores for clinical and research purposes. In addition, the meaning of a score from the mDGI, regardless of whether at the task, performance facet, or total score level, was comparable across the 5 diagnostic groups, suggesting that the mDGI measured mobility function independent of medical diagnosis.

Expanding the scoring system for the Dynamic Gait Index.

BACKGROUND: The Dynamic Gait Index (DGI) measures the capacity to adapt gait to complex tasks. The current scoring system combining gait pattern (GP) and level of assistance (LOA) lacks clarity, and the test has a limited range of measurement. OBJECTIVE: This study developed a new scoring system based on 3 facets of performance (LOA, GP, and time) and examined the psychometric properties of the modified DGI (mDGI). DESIGN: A cross-sectional, descriptive study was conducted. METHODS: Nine hundred ninety-five participants (855 patients with neurologic pathology and mobility impairments [MI group] and 140 patients without neurological impairment [control group]) were tested. Interrater reliability was calculated using kappa coefficients. Internal consistency was computed using the Cronbach alpha coefficient. Factor analysis and Rasch analysis investigated unidimensionality and range of difficulty. Internal validity was determined by comparing groups using multiple t tests. Minimal detectable change (MDC) was calculated for total score and 3 facet scores using the reliability estimate for the alpha coefficients. RESULTS: Interrater agreement was strong, with kappa coefficients ranging from 90% to 98% for time scores, 59% to 88% for GP scores, and 84% to 100% for LOA scores. Test-retest correlations (r) for time, GP, and LOA were .91, .91, and .87, respectively. Three factors (time, LOA, GP) had eigenvalues greater than 1.3 and explained 79% of the variance in scores. All group differences were significant, with moderate to large effect sizes. The 95% minimal detectable change (MDC95) was 4 for the mDGI total score, 2 for the time and GP total scores, and 1 for the LOA total score. LIMITATIONS: The limitations included uneven sample sizes in the 2 groups. The MI group were patients receiving physical therapy; therefore, they may not be representative of this population. CONCLUSIONS: The mDGI, with its expanded scoring system, improves the range, discrimination, and facets of measurement related to walking function. The strength of the psychometric properties of the mDGI warrants its adoption for both clinical and research purposes.