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Updated: May 10, 2026
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Published on: August 8, 2019
The development of the de morton mobility index (DEMMI) in an older acute medical population: item reduction using
Natalie A de Morton1, Megan Davidson, Jennifer L Keating
1Donvale Rehabilitation Hospital, 1119 Doncaster Rd., VIC 3111, Australia. demortonn@ramsayhealth.com.au
Abstract:
The DEMMI (de Morton Mobility Index) is a new and advanced instrument for measuring the mobility of all older adults across clinical settings. It overcomes practical and clinimetric limitations of existing mobility instruments. This study reports the process of item reduction using the Rasch model in the development of the DEMMI. Prior to this study, qualitative methods were employed to generate a pool of 51 items for potential inclusion in the DEMMI. The aim of this study was to reduce the item set to a unidimensional subset of items that ranged across the mobility spectrum from bed bound to high levels of independent mobility. Fifty-one physical performance mobility items were tested in a sample of older acute medical patients. A total of 215 mobility assessments were performed. Seventeen mobility items that spanned the mobility spectrum were selected for inclusion in the new instrument. The 17 item scale fitted the Rasch model. Items operated consistently across the mobility spectrum regardless of patient age, gender, cognition, primary language or time of administration during hospitalisation. Using the Rasch model, an interval level scoring system was developed with a score range of 0 to 100.
Insights
The de Morton Mobility Index (DEMMI) was developed using Rasch modeling to create a reliable mobility measure for older adults. This 17-item scale effectively assesses mobility across a wide spectrum, from bed-bound to independent living.
Area of Science:
- Gerontology
- Rehabilitation Science
- Psychometrics
Background:
- Existing mobility instruments for older adults have practical and clinimetric limitations.
- A need exists for a comprehensive and valid measure of mobility across diverse clinical settings.
- The de Morton Mobility Index (DEMMI) was developed to address these limitations.
Purpose of the Study:
- To report the item reduction process using Rasch modeling for the development of the DEMMI.
- To select a unidimensional subset of items covering the full mobility spectrum.
- To establish an interval-level scoring system for the DEMMI.
Main Methods:
- Qualitative methods generated an initial pool of 51 mobility items.
- The Rasch model was applied to reduce the item set based on data from 215 mobility assessments in older acute medical patients.
- Item fit and targeting across the mobility spectrum were evaluated.
Main Results:
- Seventeen mobility items spanning the spectrum from bed-bound to high independence were selected.
- The 17-item DEMMI demonstrated good fit to the Rasch model.
- Items operated consistently across different patient demographics and hospitalisation times.
- An interval-level scoring system (0-100) was developed using the Rasch model.
Conclusions:
- The Rasch model effectively reduced the item pool to create a unidimensional mobility measure.
- The 17-item DEMMI is a valid and reliable instrument for assessing mobility in older adults across clinical settings.
- The DEMMI provides an interval-level score, enhancing its utility in clinical practice and research.