Validation of a performance-based IADL summary measure to identify difficulties in complex activities of daily living, cognitive functions, and subsequent disability: Results from the Women's Health and Aging Study II (WHAS II)

By the year 2050, an estimated 13.2 million persons will be diagnosed with Alzheimer's disease using the 2000 Census. A study by Suh et al. indicated that IADL were hierarchically most vulnerable in the early stage of AD, which suggested the need for early interventions in high-functioning subjects to preserve their highest level of functional capability. With early detection and identification, early intervention or compensatory strategies can be employed to intervene on or delay further deterioration.; The overall aim of this dissertation was to validate a composite IADL summary measure to identify difficulties in complex everyday tasks, and examine its association with cognitive functions and disabilities.; In Chapter 4, we validate the IADL summary measure via several procedures to test its psychometric utility. For example, content validity was tested through the calculation of the intraclass correlation coefficient (ICC) to examine the domain of content in the IADL summary measure. Then, we evaluated the construct validity by comparing the IADL summary score by level of self-report difficulty concurrently. Criterion validity was tested with the assistance of Receiver Operating Characteristics (ROC) Curve analysis attempting to identify a cutoff value which appeared to present the largest area under the curve (AUC) with highest sensitivity and better specificity. The results from procedures above indicated that this IADL summary measure is a valid tool in identifying difficulty in complex activities of daily living.; In Chapter 5, we examine the relationships between the IADL summary measure and cognitive functions across different domains associated with dementia. The results suggested that the IADL summary measure is strongly associated with each individual cognitive measure, such as memory, executive function, and psychomotor speed. Finally, in Chapter 6, we further investigate the relationship between the IADL summary measure and domains of disability. The results indicated that the IADL summary measure is more strongly associated with performance-based tests than self-report methods. Findings from Chapters 3, 4, and 5 offer intriguing evidence that the IADL summary measure is a valid tool in identifying difficulties in higher functioning activities of daily living, and is highly associated with cognitive functions and disability.