Questioning the Meaning of a Change on the Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog): Noncomparable Scores and Item-Specific Effects Over Time
Abstract
Longitudinal invariance indicates that a construct is measured over time in the same way, and this fundamental scale property is a sine qua non to track change over time using ordinary mean comparisons. The Alzheimer’s Disease Assessment Scale–cognitive (ADAS-Cog) and its subscale scores are often used to monitor the progression of Alzheimer’s disease, but longitudinal invariance has not been formally evaluated. A configural invariance model was used to evaluate ADAS-Cog data as a three correlated factors structure for two visits over 6 months, and four visits over 2 years (baseline, 6, 12, and 24 months) among 341 participants with Alzheimer’s disease. We also attempted to model ADAS-Cog subscales individually, and furthermore added item-specific latent variables. Neither the three-correlated factors ADAS-Cog model, nor its subscales viewed unidimensionally, achieved longitudinal configural invariance under a traditional modeling approach. No subscale achieved scalar invariance when considered unidimensional across 6 months or 2 years of assessment. In models accounting for item-specific effects, configural and metric invariance were achieved for language and memory subscales. Although some of the ADAS-Cog individual items were reliable, comparisons of summed ADAS-Cog scores and subscale scores over time may not be meaningful due to a lack of longitudinal invariance.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- May 14, 2020
- Source ID
- 10.1177/1073191120915273
Entities
People
- Bradley J. Macintosh
- Hugo Cogo-Moreira
- Krista L. Lanctôt
- Michael Eid
- Nathan Herrmann
- Saffire H Krance
- Sandra E. Black
- Walter Swardfager
Organizations
- Alexander von Humboldt Foundation
- Freie Universität Berlin
- National Institutes of Health
- Sunnybrook Research Institute
- United States Department of Defense
- Universidade Federal de São Paulo
- University of Toronto