Author Type

Graduate Student

Date of Award

Summer 7-21-2026

Document Type

Dissertation

Publication Status

Version of Record

Submission Date

August 2026

Department

Psychology

College Granting Degree

Charles E. Schmidt College of Science

Department Granting Degree

Psychology

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Mónica Rosselli

Abstract

Some older adults score differently on the same cognitive test from one visit to the next, and that inconsistency has been proposed as an early warning sign of decline. This dissertation tested whether within-person variability actually tells us anything useful about who has, or will develop, mild cognitive impairment (MCI). A total of 334 older adults completed quarterly neuropsychological testing over three years as part of a larger longitudinal study. Visit-to-visit variability was measured as the mean absolute successive difference on the MoCA, the MMSE, and a battery of memory, executive, language, and visuospatial tasks, and MCI was classified from the Clinical Dementia Rating. The five aims examined the variability of global screening scores and its demographic correlates, compared the MoCA and MMSE, evaluated whether variability in specific cognitive domains predicted MCI, tested whether these patterns differed by sex, and investigated whether early variability predicted later conversion. Analyses included correlation, regression, linear mixed-effects models, logistic regression, and survival models.

Variability increased with age but had no relationship to education or sex once age was accounted for. MoCA scores fluctuated more than MMSE scores, yet the MMSE separated MCI from normal cognition slightly better. Of fourteen variability indices, only four flagged MCI, and all four came from executive-function and learning tasks rather than the semantic-memory measures that were expected to matter. Men were somewhat more variable than women on a few measures, but sex never changed the relationship between variability and MCI. Early variability did not predict who later converted to MCI, but it reflected only the instability in the clinical ratings themselves. The intraindividual variability was a real but limited marker, associated with current cognitive status, most clearly in executive and learning performance, but it did not predict decline over time and showed no meaningful sex differences. It only offers a modest additional information beyond the measures clinicians already use.

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