Intra-individual cognitive variability predicts the trajectory of longitudinal neurocognitive and functional decline

<b>Objective:</b> Intra-individual cognitive variability (IICV) has been found to predict cognitive decline and dementia incidence among older adults based on a one follow-up testing paradigm while the association between IICV and daily functioning is less studied. The current study intended to investigate the predictability of IICV on the trajectory of decline in cognition and self-report daily functioning among older adults, tracked with multiple time points. <b>Method:</b> The current study employed a diverse, longitudinal, archival data set from the Rush Alzheimer's Disease Center (<i>N</i> = 4,319) and examined 5 waves of data with growth curve modeling. Multiple sensitivity analyses were followed up to scrutinize the robustness of study results, accounting for demographic covariates, baseline mean cognitive performance, skewness, and attrition. <b>Results:</b> Results supported the main hypothesis that the trend of IICV predicted the trajectory of cognition, <i>β</i> = .-57, <i>p</i> = .002, and self-reported daily functioning, β = .48, <i>p</i> = .037, and the results were robust against the inclusion of covariates, skewness, and attrition. <b>Conclusions:</b> With a rigorous methodology and statistical approach, the current study contributed to the scientific and medical understanding of IICV and lent support to the clinical use of IICV in neuropsychological assessment. Methodological strengths and limitations were noted.