Clinimetric Properties of the de Morton Mobility Index in Healthy, Community-Dwelling Older Adults

Abstract

Davenport SJ, de Morton NA. Clinimetric properties of the de Morton Mobility Index in healthy, community-dwelling older adults. Objective To investigate the clinimetric properties of the de Morton Mobility Index (DEMMI) in healthy, community-dwelling older adults. Design Cohort study. Setting Retirement village and Returned and Services League (RSL) club in Melbourne, Australia. Participants All participants were 65 years or older, healthy, and living within the community. The validation study included participants recruited from a retirement village (n=61), and the reliability studies included participants recruited from an RSL club and a subset of participants from the retirement village. Interventions Not applicable. Main Outcome Measures Mobility was assessed using the DEMMI. The percentage of participants who scored the highest and lowest possible score on the DEMMI was calculated to determine whether a floor or ceiling effect occurred. The minimal clinically important difference (MCID) was estimated using a distribution-based method. Reliability was assessed independently and concurrently using the minimal detectable change at 90% confidence (MDC 90). Results Evidence of convergent and discriminant validity was obtained for the DEMMI by examining correlations with measures of related constructs, the Lower Extremity Functional Scale ( r=.69) and Quality of Life Scale scores ( r=.28), respectively. Participants who ambulated without a gait aid (82.62±10.63) had significantly higher ( P<.0) DEMMI scores than those who ambulated with an aid (64.1±12.40), providing evidence of known groups validity. No floor or ceiling effect was identified. The MCID was 7 points. The MDC 90 was 13 (95% CI, 8.76–17.05) points on the 100-point scale. Conclusion DEMMI scores in healthy, community-dwelling older adults are both valid and reliable.