Assessing the Validity of the Dynamic Gait Index in a Balance Disorders Clinic: An Application of Rasch Analysis

Background. The Dynamic Gait Index (DGI) has emerged as a valid indicator of functional gait abilities for people with balance and vestibular disorders. Recent Rasch-based analyses have indicated possible concerns for multidimensionality and a ceiling effect within the DGI. Objective. The aim of this study was to evaluate the DGI in a sample of patients. from a dizziness and balance clinic to determine whether patient features such as dizziness or fall history influence the measurement characteristics of the DGI. Design. This study used a retrospective design. Methods. A sample of 117 patients' charts was reviewed, and patients were grouped according to a primary impairment of dizziness only or imbalance and were categorized based on a history of falls. A one-parameter Rasch-Andrich rating scale model was used with thorough analyses, including rating scale analysis, item-difficulty hierarchy, scale unidimensionality, and differential item functioning (DIF). Results. The DGI demonstrated an effective rating scale design and was found to be a unidimensional measurement of dynamic gait. The DGI displayed a modest ceiling effect, primarily with patients with higher functional levels displaying symptoms of dizziness. Three items ("vertical head nods," "gait on level surface," and "stepping over obstacles") demonstrated DIF based on categories of patient characteristics, although the effects on measurement were negligible. Limitations. Functional categories were based on impairments and not underlying medical diagnoses derived from a retrospective chart review, whereas the limited sample size may have underestimated statistically significant DIF. Conclusions. Results from this study offer additional evidence supporting the validity of the DGI as a measure of gait ability. The present findings also are in agreement with prior research that has shown a ceiling effect for the DGI in people with balance or vestibular disorders. Effects of DIF were found to be negligible, yet the presence of DIP within the present sample helped to explain some differences in DGI item-difficulty hierarchies from prior studies. Continued research is needed to determine how population differences may affect performance on the DGI and to develop and test assessments capable of measuring a broader range of gait abilities.