Measuring mobility in older hospital patients with cognitive impairment using the de Morton Mobility Index

BACKGROUND: Mobility is a key outcome in older patients with cognitive impairment. The de Morton Mobility Index (DEMMI) is an established measure of older people’s mobility that is promising for use in older patients with cognitive impairment. The aim of this study was to examine the DEMMI’s psychometric properties in older patients with dementia, delirium or other cognitive impairment. METHODS: This cross-sectional study was performed in a geriatric hospital and includes older acute medical patients with cognitive impairment indicated by a Mini Mental State Examination (MMSE) score ≤ 24 points. A Rasch analysis was performed to check the DEMMI’s unidimensionality. Construct validity was assessed by testing 13 hypotheses about expected correlations between the DEMMI and outcome measures of similar or related constructs, and about expected differences of DEMMI scores between groups differing in mobility related characteristics. Administration times were recorded. RESULTS: A sample of 153 patients with mild (MMSE 19–24 points; 63%) and moderate (MMSE: 10–18 points; 37%) cognitive impairment was included (age range: 65–99 years; mean MMSE: 19 ± 4, range: 8–24 points; diagnosis of dementia and delirium: 40% and 18%, respectively). Rasch analysis indicated unidimensionality with an overall fit to the model (P = 0.107). Internal consistency reliability was excellent (Cronbach’s alpha = 0.92). Eleven out of 13 (85%) hypotheses on construct validity were confirmed. The DEMMI showed good feasibility, and no adverse events occurred. The mean administration time of 5 min (range: 1–10) was not influenced by the level of cognitive impairment. In contrast to some other comparator instruments, no floor or ceiling effects were evident for the DEMMI. CONCLUSIONS: Results indicate sufficient psychometric properties of the DEMMI in older patients with cognitive impairment. TRIAL REGISTRATION: German Clinical Trials Register (DRKS00005591). Registered February 2, 2015. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12877-018-0780-9) contains supplementary material, which is available to authorized users.