A generic outcome assessment of mobility capacity in neurorehabilitation: measurement properties of the de Morton Mobility Index

Abstract

\n Background: Mobility capacity is a key outcome domain in neurorehabilitation. The de Morton Mobility Index (DEMMI), an established and generic outcome assessment of mobility in older patients, is promising for use in neurorehabilitation.Objective: To examine the measurement properties of the DEMMI in rehabilitation inpatients with neurological conditions.Methods: Cross-sectional study including a mixed sample of adult inpatients in a neurorehabilitation hospital. Structural validity, unidimensionality and measurement invariance (Rasch analysis), construct validity, internal consistency reliability, and inter-rater reliability of the DEMMI (scale range: 0–100 points) were established. The minimal detectable change, the 95% limits of agreement, and possible floor and ceiling effects were calculated to indicate interpretability. Results: We analyzed validity (n = 348) and reliability (n = 133) in two samples. In both samples, the majority of participants had a sub-acute stroke or Parkinson’s disease. Rasch analysis indicated unidimensionality with an overall fit to the model (chi-square = 59.4, P = 0.074). There was no relevant measurement invariance by disease group. All 11 hypotheses on construct validity were confirmed. Internal consistency reliability (Cronbach’s alpha = 0.94) and inter-rater reliability (intraclass correlation coefficient = 0.94; 95% confidence interval: 0.91–0.95) were sufficient. The minimal detectable change with 90% confidence was 15.0 points and the limits of agreement were 39%. No floor or ceiling effects were observed. Conclusions: Results indicate sufficient measurement properties of the DEMMI in rehabilitation inpatients with neurological conditions. The DEMMI can be used as a generic outcome assessment of mobility capacity in neurorehabilitation.Trial registration: German Clinical Trials Register (DRKS00004681). Registered May 6, 2013.