Reliability of mobility measures in older medical patients with cognitive impairment

Tobias Braun,Ralf-Joachim Schulz,Christian Thiel,Christian Grüneberg

doi:10.1186/s12877-019-1036-z

Abstract

BackgroundMobility is a key indicator of physical functioning in older people, but there is limited evidence of the reliability of mobility measures in older people with cognitive impairment. This study aimed to examine the test-retest reliability and measurement error of common measurement instruments of mobility and physical functioning in older patients with dementia, delirium or other cognitive impairment.MethodsA cross-sectional study was performed in a geriatric hospital. Older acute medical patients with cognitive impairment, indicated by a Mini-Mental State Examination (MMSE) score of ≤24 points, were assessed twice within 1 day by a trained physiotherapist.The following instruments were applied: de Morton Mobility Index, Hierarchical Assessment of Balance and Mobility, Performance-Oriented Mobility Assessment, Short Physical Performance Battery, 4-m gait speed, 5-times chair rise test, 2-min walk test, timed up and go test, Barthel Index mobility subscale and Functional Ambulation Categories.As appropriate, the intraclass correlation coefficient (ICC), Cohen’s kappa, standard error of measurement, limits of agreement and minimal detectable change (MDC) values were estimated.ResultsSixty-five older acute medical patients with cognitive impairment participated in the study (mean age: 82 ± 7 years; mean MMSE: 20 ± 4, range: 10 to 24 points). Some participants were physically or cognitively unable to perform the gait speed (46%), 2-min walk (46%), timed up and go (51%) and chair rise (75%) tests.ICC and kappa values were above 0.9 in all instruments except for the gait speed (ICC = 0.86) and chair rise (ICC = 0.72) measures. Measurement error is reported for each instrument. The absolute limits of agreement ranged from 11% (de Morton Mobility Index and Hierarchical Assessment of Balance and Mobility) to 35% (chair rise test).ConclusionsThe test-retest reliability is sufficient (> 0.7) for group-comparisons in all examined instruments. Most mobility measurements have limited use for individual monitoring of mobility over time in older hospital patients with cognitive impairment because of the large measurement error (> 20% of scale width), even though relative reliability estimations seem sufficient (> 0.9) for this purpose.Trial registrationGerman Clinical Trials Register (DRKS00005591). Registered 2 February 2015.

Highlights

Mobility is a key indicator of physical functioning in older people, but there is limited evidence of the reliability of mobility measures in older people with cognitive impairment
Thirty-seven percent of participants were diagnosed with dementia, while 17% were diagnosed with delirium
The results indicate sufficient test-retest reliability for group-comparisons of the de Morton Mobility Index (DEMMI), Hierarchical Assessment of Balance and Mobility (HABAM), Performance Oriented Mobility Assessment (POMA), Short Physical Performance Battery (SPPB), 2-min walk test, Timed up and go test (TUG), Barthel Index mobility subscale and Functional Ambulation Categories (FAC) in older acute medical patients with cognitive impairment

Summary

Introduction

Mobility is a key indicator of physical functioning in older people, but there is limited evidence of the reliability of mobility measures in older people with cognitive impairment. This study aimed to examine the test-retest reliability and measurement error of common measurement instruments of mobility and physical functioning in older patients with dementia, delirium or other cognitive impairment. Mobility is a key indicator of physical functioning in older people, and common measures of mobility, such as gait speed or the timed up and go test (TUG), are used to assess these outcomes. To monitor alterations in mobility, clinicians depend on reliable measurement instruments to provide trustworthy test scores over time (change scores). Test-retest reliability (relative reliability) concerns the extent to which scores of patients who have not changed are the same for repeated measurement over time [2]. The MDC is defined as a change beyond measurement error; it “represents the spread of the distribution of change scores that would be expected if no true change had occurred” [4]

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