Parallel but not equivalent: Challenges and solutions for repeated assessment of cognition over time

• Published in: Journal of clinical and experimental neuropsychology 2012-01, Vol.34 (7), p.758-772
• Main Authors: Gross, Alden L., Inouye, Sharon K., Rebok, George W., Brandt, Jason, Crane, Paul K., Parisi, Jeanine M., Tommet, Doug, Bandeen-Roche, Karen, Carlson, Michelle C., Jones, Richard N.
• Format: Article
• Language: English
• Subjects: Aged; Aged, 80 and over; Alternate forms; Alzheimer's disease; Biological and medical sciences; Cognition; Cognition Disorders - diagnosis; Cognition Disorders - psychology; Equating; Equipercentile; Female; Humans; Individuality; Longitudinal analysis; Longitudinal Studies; Male; Medical sciences; Neuropsychological Tests; Neuropsychology; Parallel forms; Psychology. Psychoanalysis. Psychiatry; Psychometrics. Diagnostic aid systems; Psychopathology. Psychiatry; Techniques and methods; Verbal Learning
• ISSN: 1380-3395; 1744-411X
• DOI: 10.1080/13803395.2012.681628

Objective. Analyses of individual differences in change may be unintentionally biased when versions of a neuropsychological test used at different follow-ups are not of equivalent difficulty. This study's objective was to compare mean, linear, and equipercentile equating methods and demonstrate their utility in longitudinal research. Study design and setting: The Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE, N = 1,401) study is a longitudinal randomized trial of cognitive training. The Alzheimer's Disease Neuroimaging Initiative (ADNI, n = 819) is an observational cohort study. Nonequivalent alternate versions of the Auditory Verbal Learning Test (AVLT) were administered in both studies. Results. Using visual displays, raw and mean-equated AVLT scores in both studies showed obvious nonlinear trajectories in reference groups that should show minimal change and poor equivalence over time (ps ≤ .001), and raw scores demonstrated poor fits in models of within-person change (root mean square errors of approximation, RMSEAs > 0.12). Linear and equipercentile equating produced more similar means in reference groups (ps ≥ .09) and performed better in growth models (RMSEAs < 0.05). Conclusion. Equipercentile equating is the preferred equating method because it accommodates tests more difficult than a reference test at different percentiles of performance and performs well in models of within-person trajectory. The method has broad applications in both clinical and research settings to enhance the ability to use nonequivalent test forms.