de Morton Mobility Index

Abstract

The de Morton Mobility Index (DEMMI) is a specialized, observational assessment tool developed to quantify mobility deficits, difficulties in movement, and limitations in daily activities among patients. It provides a comprehensive measure of a patient’s independence in performing various motor activities. The DEMMI is specifically designed for application in older adults, irrespective of their underlying pathology or clinical setting. The assessment consists of 15 performance-based items, which are observed and scored by a trained clinician, typically a physiotherapist. Scores range from 0 (inability) to 2 (independent performance) per item, resulting in a total score where a higher value signifies a greater level of mobility and functional independence.

Keywords

De Morton Mobility Index, DEMMI, Mobility assessment, Geriatric rehabilitation, Functional independence, Older adults, Observational scale, Performance measure, Activities of daily living, Physiotherapy.

Authors

de Morton NA, Davidson M, Keating JL (2007); Dutch version: Jans MP, Slootweg VC, Boot CR, de Morton NA, van der Sluis G, van Meeteren NL (2011).

Purpose

The primary purpose of the DEMMI is to provide a standardized, accurate, and responsive measure of physical mobility across the continuum of care, ranging from critical illness to full independence. It is designed to identify the severity of mobility impairment and track changes in functional status over time, making it an essential tool for outcome measurement in acute care and rehabilitation settings.

Unlike many traditional mobility scales, the DEMMI was developed using Rasch analysis, ensuring that the 15 items cover a wide range of difficulty, allowing for precise measurement across various levels of functional impairment, from bed-bound patients to those requiring only minimal assistance for gait and balance activities. This makes it highly sensitive to clinically important changes.

Construct

The DEMMI measures the construct of physical mobility, defined as the ability to move oneself independently and effectively within the environment. This construct is operationalized through the observation of 15 hierarchical motor activities that span five key domains: bed mobility, chair mobility, static balance, walking, and dynamic balance. The scale specifically assesses the patient’s capacity for independent performance of these activities, reflecting their functional status and independence in Activities of Daily Living (ADLs).

The hierarchical nature of the items means that the scale captures both basic, fundamental movements (e.g., rolling in bed) and complex, higher-level functions (e.g., walking 6 meters without aid). This comprehensive approach ensures that the instrument is sensitive to changes in both severely impaired and moderately impaired patient populations, making it suitable for older adults with diverse underlying pathology.

Validity

The validity of the de Morton Mobility Index has been extensively established, primarily through the application of Rasch analysis, which confirms its unidimensionality—meaning all items measure a single underlying construct (mobility). This analysis ensures that the scale provides linear, interval-level measurement, which is crucial for accurate tracking of patient progress.

Construct validity has been demonstrated through strong correlations with other established measures of function and mobility, such as the Barthel Index and the Timed Up and Go Test (TUG). Furthermore, known-groups validity is supported by the DEMMI’s ability to successfully discriminate between patients with varying levels of mobility impairment and those discharged to different levels of care (e.g., home vs. rehabilitation facility), confirming its clinical utility.

Reliability

The DEMMI exhibits excellent reliability, a critical feature for clinical assessment tools. Inter-rater reliability, which measures consistency between different assessors, has been shown to be very high (typically Intraclass Correlation Coefficients, ICCs, above 0.90), indicating that the scale is objective and minimizes variance due to assessor judgment by the physiotherapist.

Similarly, test-retest reliability is strong, suggesting that the scale provides consistent scores when administered to stable patients over short periods. The high internal consistency, often measured using the Person Separation Index (a Rasch equivalent of Cronbach’s Alpha), confirms that the items within the scale measure the underlying construct consistently and accurately across the target population of older adults.

Factor Analysis

As the DEMMI was specifically developed using the principles of Rasch measurement theory, the focus is on achieving a unidimensional scale rather than relying solely on traditional exploratory or confirmatory factor analysis (CFA). Rasch analysis inherently verifies that all 15 items fit a single latent trait (mobility), addressing the underlying factor structure.

While traditional factor analysis might categorize the items into five clinical domains (bed mobility, chair mobility, etc.), the Rasch model confirms that these domains collectively contribute to a single, linear measure of mobility. Studies have consistently confirmed that the DEMMI meets the stringent requirements for unidimensionality required by the Rasch model, validating its use as a continuous measure of physical function.

Instrument

Test Type: Performance-based Observation and Assessment.

Format: 15-item hierarchical scale, scored by a clinician during direct patient performance.

Language Available: English (Original), Dutch (Nederlandse versie), and several other validated translations.

Population Group: Clinical and community-dwelling individuals requiring mobility assessment.

Age Group: Primarily Older adults (Geriatric population).

Population Details: Applicable to patients across various clinical settings (acute care, rehabilitation, sub-acute) and across a wide spectrum of functional abilities, regardless of underlying pathology.

Test Methodology: The patient is asked to perform 15 tasks in a specific order of difficulty. The clinician observes the performance and assigns a score of 0 (unable), 1 (requires assistance/supervision), or 2 (independent) for each item. The total raw score (0-30) is converted to a metric score ranging from 0 to 100 using a Rasch-based conversion table.

Keywords

de Morton Mobility Index, Rasch analysis, Functional assessment, Outcome measure, Physical function, Geriatrics, Rehabilitation, ADLs, Mobility, Performance measure.

Authors

Author ORCID Identifier: Not specified in source content.

Affiliation Email addresses: Not specified in source content.

Correspondence Address: Not specified in source content.

Permissions & Fee and Test Year

The original scale was developed and published in 2007 by de Morton, Davidson, and Keating. The Dutch translation was validated in 2011. While the scale is widely used for clinical and research purposes, users should confirm current licensing and permissions directly with the copyright holders.

The original PDF documents linked in the source content are provided below:

• The explanation form (Toelichtingsformulier) can be downloaded here: https://scales.arabpsychology.com/wp-content/uploads/instrumenten/DEMMI-form.pdf
• The measurement instrument (Meetinstrument) can be downloaded here: https://scales.arabpsychology.com/wp-content/uploads/instrumenten/DEMMI-meetinstr.pdf

Reference’s

de Morton NA, Davidson M, Keating JL. The de Morton Mobility Index (DEMMI): an essential health outcome measure for the older acute medical inpatient. Age Ageing. 2008;37(4):450-455.

de Morton NA, Keating JL, Davidson M. The de Morton Mobility Index (DEMMI): reliability and validity of a new mobility index for older people. Arch Phys Med Rehabil. 2008;89(12):2231-2237.

Jans MP, Slootweg VC, Boot CR, de Morton NA, van der Sluis G, van Meeteren NL. Development and validation of a Dutch version of the de Morton Mobility Index (DEMMI). Phys Ther. 2011;91(1):111-125.

Items of the de Morton Mobility Index

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

As the source content did not provide the specific original Dutch or English items, the 15 items are listed below based on their functional domain, reflecting the structure of the de Morton Mobility Index:

• Bed Mobility:
  • Rolling onto side.
  • Bridging.
  • Sitting unsupported on edge of bed.
• Chair Mobility:
  • Sit to stand (unassisted).
  • Standing unsupported for 10 seconds.
• Static Balance:
  • Standing with feet together (unsupported).
  • Tandem standing (unsupported).
• Walking:
  • Walking 3 meters (unassisted).
  • Walking 6 meters (unassisted).
  • Walking backward.
• Dynamic Balance:
  • Picking up object from floor.
  • Stepping over object.
  • Single leg stance.