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Setting the minimal metrically detectable change on disability rating scales
R Hébert1, D J Spiegelhalter, C Brayne
1Gerontology and Geriatrics Research Centre, Sherbrooke Geriatric University Institute, Sherbrooke, Québec, Canada.
Archives of Physical Medicine and Rehabilitation
|January 9, 1998
Summary
The minimal metrically detectable change (MMDC) on disability scales was determined using psychometric and empirical methods. The empirical method established an MMDC of 5 points, useful for clinical trial interpretation.
Area of Science:
- Gerontology
- Health Services Research
- Biostatistics
Background:
- Establishing the minimal metrically detectable change (MMDC) is crucial for interpreting score variations in rating scales.
- Two primary methods, psychometric and empirical, exist for determining MMDC.
Purpose of the Study:
- To compare the MMDC derived from a psychometric method (using external reliability) with an empirical method (using longitudinal data).
- To assess the MMDC for the Functional Autonomy Measuring System (SMAF) in older adults.
Main Methods:
- A longitudinal survey design was employed with a representative sample of 572 community-dwelling adults aged over 75.
- Disability was measured using the Functional Autonomy Measuring System (SMAF).
- The psychometric method utilized reliability coefficients from external and internal stable subsamples, while the empirical method examined score variability in a stable subsample.
Main Results:
- The psychometric method yielded MMDC values of 3.7 (external reliability) and 5.2 (internal reliability).
- The empirical method established an MMDC of 5 points on the SMAF.
- A notable difference was observed between the psychometric and empirical approaches.
Conclusions:
- The empirical method provides a robust MMDC for the SMAF in older adults.
- Setting the MMDC is valuable for sample size calculations and interpreting clinical trial outcomes.
- The MMDC serves as a benchmark for the minimal clinically important difference.