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

BACKGROUND: Mobility capacity is a key outcome domain in neurorehabilitation. The de Morton Mobility Index (DEMMI), an established and generic outcome assessment of mobility capacity in older patients, is promising for use in neurorehabilitation. The aim of this study was 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. Hypotheses-based correlation analyses (DEMMI and other functional outcome assessments) showed sufficient construct validity. 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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12883-021-02327-0.