Non-parametric item response theory applications in the assessment of dementia
View/ Open
McGrory2015.docx (7.147Mb)
Date
30/06/2015Author
McGrory, Sarah
Metadata
Abstract
This thesis sought to address the application of non-parametric item response theory (NIRT)
to cognitive and functional assessment in dementia. Performance on psychometric tests is key
to diagnosis and monitoring of dementia. NIRT can be used to improve the psychometric
properties of tests used in dementia assessment in multiple ways: confirming an underlying
unidimensional structure, establishing formal item hierarchical patterns of decline, increasing
insight by examining item parameters such as difficulty and discrimination, and creating
shorter tests. From a NIRT approach item difficulty refers to the ease with which an item is
endorsed. Discrimination is an index of how well an item can differentiate between patients
of varying levels of severity.
Firstly I carried out a systematic review to identify applications of both parametric
and non-parametric IRT to measures assessing global cognitive functioning in people with
dementia. This review demonstrated that IRT can increase the interpretive power of cognitive
assessment scales and confirmed the limited number of IRT analyses of cognitive scales in
dementia populations. This thesis extended this approach by applying Mokken scaling
analysis to commonly used measures of current cognitive ability (Addenbrooke’s Cognitive
Examination-Revised (ACE-R)) and of premorbid cognitive ability (National Adult Reading
Test (NART)). Differential item functioning (DIF) by diagnosis identified slight variations in
the patterns of hierarchical decline in the ACE-R. These disease-specific sequences of decline
could serve as an adjunct to diagnosis, for example where learning a name and address is a
more difficult task than being orientated in time, late onset Alzheimer’s disease is a more
probable diagnosis than mixed Alzheimer’s and vascular dementia. These analyses also
allowed key items to be identified which can be used to create briefer scales (mini-ACE and
Mini-NART) which have good psychometric properties. These scales are clinically relevant,
comprising highly discriminatory, invariantly ordered items. They also allow sensitive
measurement and adaptive testing and can reduce test administration time and patient stress.
Impairment of functional abilities represents a crucial component of dementia
diagnosis with performance on these functional tasks predictive of overall disease. A second
aspect of this thesis, therefore, was the application of Mokken scaling analyses to measures of
functional decline in dementia, specifically the Lawton Instrumental Activities of Daily
Living (IADL) scale and Physical Self-Maintenance Scale (PSMS). While gender DIF was
observed for several items, implying the likelihood of equal responses from men and women
is not equal a generally consistent pattern of impairment in functional ability was observed
across different types of dementia.
Collections
The following license files are associated with this item: