Greater precision when measuring dementia severity: establishing item parameters for the Clinical Dementia Rating Scale.

BACKGROUND/AIMS: An item response theory (IRT)-based scoring approach to the Clinical Dementia Rating Scale (CDR) can account for the pattern of scores across the CDR items (domains) and their differential abilities to indicate dementia severity. In doing so, an IRT-based approach can provide greater precision than other CDR scoring algorithms. However, neither a good set of item parameters nor an easily digestible set of instructions needed to implement this approach is readily available. METHODS: Participants were 1,326 patients at the Baylor College of Medicine Alzheimer's Disease and Memory Disorders Clinic. RESULTS: The item parameters necessary for an IRT-based scoring approach were identified (a parameters ranged from 3.01 to 6.22; b parameters ranged from -2.46 to 2.07). CONCLUSION: This study provides, and demonstrates how to easily apply, IRT-based item parameters for the CDR

Item response theory reveals variability of functional impairment within clinical dementia rating scale stages.

BACKGROUND/AIMS: To investigate whether an item response theory (IRT) approach to measuring variations of dementia severity within Clinical Dementia Rating (CDR) stages is associated with activities of daily living (ADLs). METHODS: IRT estimates of dementia severity within CDR stages in 1,181 patients were correlated with ADLs and analyzed. RESULTS: IRT-determined dementia severity was significantly correlated with ADLs in three of four impaired dementia stages. CONCLUSION: An IRT approach shows considerable advantages over traditional scoring practices of the CDR not only because it increases precision in dementia measurement, but also because it enables one to discover more precise associations with functional outcomes such as ADLs.

Item Response Theory Analysis of the Texas Functional Living Scale.

OBJECTIVE: The Texas Functional Living Scale (TFLS) is a performance-based measure of functional abilities assessing the domains of time, money and calculation, communication, and memory. It is likely that certain items are more sensitive at different levels of functional impairment, with some signaling milder degrees of functional difficulty. This study analyzed psychometric characteristics of individual TFLS items using item response theory (IRT) in an outpatient clinical sample. METHOD: In total, 270 adult outpatients completed the TFLS during clinical neuropsychological evaluation. IRT analysis using 2PL and graded response model was applied to the TFLS. RESULTS: Item parameters, item characteristic curves, and information curves were produced. Item difficulty (a) parameters ranged from 1.05 to 2.23, and item discrimination (b) parameters ranged from -4.11 to 0.51. CONCLUSIONS: TFLS items were differentially sensitive along the continuum of functional impairment. Items that were most sensitive to milder degrees of functional impairment involved clock drawing, microwave programming, financial calculation, and prospective memory. Other items that were optimally precise in more severe degrees of functional impairment involved interacting with a calendar and a relatively simple financial calculation task. These findings suggest that the ability to pass at least some of the items on the TFLS may not necessarily reflect fully intact functional abilities. Certain TFLS items may be able to detect the presence of subtle functional difficulties.

Hallucinations and Delusions Signal Alzheimer's Associated Cognitive Dysfunction More Strongly Compared to Other Neuropsychiatric Symptoms.

OBJECTIVES: Neuropsychiatric symptoms (NPS) are common among individuals with dementia of the Alzheimer's type (DAT). We sought to characterize which NPS more purely relate to cognitive dysfunction in DAT, relative to other NPS. METHOD: Demographic, neurocognitive, neuroimaging, and NPS data were mined from the Alzheimer's Disease Neuroimaging Initiative database (n = 906). Using factor analysis, we analyzed the degree to which individual NPS were associated with DAT-associated cognitive dysfunction. We also employed item response theory to graphically depict the ability of individual NPS to index DAT-associated cognitive dysfunction across a continuum ranging from cognitively normal to mild DAT. RESULTS: Psychotic symptoms (hallucinations and delusions) were more strongly related to the continuum of DAT-associated cognitive dysfunction than other NPS, with the strength of the relationship peaking at high levels of disease severity. Psychotic symptoms also negatively correlated with brain volume and did not relate to the presence of vision problems. Aberrant motor behavior and apathy had relatively smaller associations with DAT-associated cognitive dysfunction, while other NPS showed minimal associations. DISCUSSION: Psychotic symptoms most strongly indexed DAT-associated cognitive dysfunction, whereas other NPS, such as depression and anxiety, were not as precisely related to the DAT-associated cognitive dysfunction.

Dual-Task Gait Assessment in a Clinical Sample: Implications for Improved Detection of Mild Cognitive Impairment.

OBJECTIVES: Research has longitudinally linked dual-task gait dysfunction to mild cognitive impairment (MCI) and dementia risk. Our group previously demonstrated that dual-task gait speed assessment distinguished between subjective cognitive complaints (SCC) and MCI in a memory clinic setting, and also found that differences in dual-task gait speed were largely attributable to executive attention processes. This study aimed to reproduce these findings in a larger diverse sample and to extend them by examining whether there were group differences in single- versus dual-task cognitive performance (number of letters correctly sequenced backward). METHOD: Two-hundred fifty-two patients (M age = 66.01 years, SD = 10.46; 119 MCI, 133 SCC) presenting with cognitive complaints in an academic medical setting underwent comprehensive neuropsychological and gait assessment (single- and dual-task conditions). RESULTS: Patients with MCI walked slower and showed greater decrement in cognitive performance than those with SCC during dual-task conditions. Neuropsychological measures of executive attention accounted for significant variance in dual-task gait performance across diagnostic groups beyond demographic and health risk factors. DISCUSSION: Reproduction of our results within a sample over four times the previous size provides support for the use of dual-task gait assessment as a marker of MCI risk in clinical settings.

Contribution of executive functioning to instrumental activities of daily living in older adults.

The Texas Functional Living Scale (TFLS) is a performance-based measure of instrumental activities of daily living (IADLs). Executive dysfunction has been linked to impairment on other IADL measures but has not been thoroughly investigated with the TFLS. This study examined the contribution of executive functioning to IADLs on the TFLS among 228 older adults (M age =76.0 +/- 6.5 years; 59% females) who completed the TFLS as part of comprehensive assessment at an outpatient neuropsychology clinic. Executive functioning measures included the Trail Making Test (TMT) Part B, the Controlled Oral Word Association Test, and the Wechsler Abbreviated Scale of Intelligence-II (WASI-II) Matrix Reasoning and Similarities subtests. Results from a hierarchical regression model revealed that only TMT Part B (ß = -.23, p = .023) and WASI-II Similarities (ß = .32, p = .002) scores significantly predicted TFLS Total scores after controlling for the contributions of demographics (i.e., age, education, and gender), and intellectual functioning and capabilities in other neurocognitive domains (i.e., WASI-II Vocabulary and Block Design subtests, TMT Part A, and Repeatable Battery for the Assessment of Neuropsychological Status Coding subtest, and the Immediate Memory, Delayed Memory, and Visuospatial/Construction Indices).

Factor Analysis of the Texas Functional Living Scale in an Outpatient Clinical Sample.

OBJECTIVE: Prior factor analysis of the Texas Functional Living Scale (TFLS), a performance-based measure of functional abilities, in a military veteran sample supported four factors discrepant from the published subscales. This study analyzed TFLS factor structure in a non-veteran clinical sample. METHOD: Two hundred seventy adult outpatients completed the TFLS during neuropsychological evaluation. Principal axis factor analysis with oblique promax rotation was conducted with age and education effects partialed out. RESULTS: Parallel analysis indicated five factors for extraction that accounted for a combined 48% of the variance. The first factor independently explained 26% of the total variance. Inspection of factor loadings suggested the following factor interpretations: complex calculations/time, complex visual search, praxis, memory, and basic calculations/math concepts. Five items did not significantly load onto any of the factors. CONCLUSIONS: Current results did not entirely correspond to the published subscales or prior results in a veteran sample. Further clarification of the TFLS factor structure is warranted.

Statistical Model of Dynamic Markers of the Alzheimer's Pathological Cascade.

Objectives: Alzheimer's disease (AD) is a progressive disease reflected in markers across assessment modalities, including neuroimaging, cognitive testing, and evaluation of adaptive function. Identifying a single continuum of decline across assessment modalities in a single sample is statistically challenging because of the multivariate nature of the data. To address this challenge, we implemented advanced statistical analyses designed specifically to model complex data across a single continuum. Method: We analyzed data from the Alzheimer's Disease Neuroimaging Initiative (ADNI; N = 1,056), focusing on indicators from the assessments of magnetic resonance imaging (MRI) volume, fluorodeoxyglucose positron emission tomography (FDG-PET) metabolic activity, cognitive performance, and adaptive function. Item response theory was used to identify the continuum of decline. Then, through a process of statistical scaling, indicators across all modalities were linked to that continuum and analyzed. Results: Findings revealed that measures of MRI volume, FDG-PET metabolic activity, and adaptive function added measurement precision beyond that provided by cognitive measures, particularly in the relatively mild range of disease severity. More specifically, MRI volume, and FDG-PET metabolic activity become compromised in the very mild range of severity, followed by cognitive performance and finally adaptive function. Conclusion: Our statistically derived models of the AD pathological cascade are consistent with existing theoretical models.

A fresh perspective revealed by powerful trends in Alzheimer's disease research.

The paper, "Ethnicity Moderates Dementia's Biomarkers", by Royall and Palmer in this issue of Journal of Alzheimer's Disease represents the cutting edge of Alzheimer's disease (AD) research. The authors capitalize on several powerful and emerging trends in AD research that will surely reap benefits for our discipline during the next decade: latent variable models, biomarkers, and ethnicity. In this study, the authors specifically find that self-reported ethnicity moderates the dementing process and hypothesize that this is more likely due to distinct biological mechanisms than environmental influences.

Adding delayed recall to the ADAS-cog improves measurement precision in mild Alzheimer's disease: Implications for predicting instrumental activities of daily living.

As research increasingly focuses on preclinical stages of Alzheimer's disease (AD), instruments must be retooled to identify early cognitive markers of AD. A supplemental delayed recall subtest for the Alzheimer's Disease Assessment Scale-cognitive (ADAS-cog; Mohs, Rosen, & Davis, 1983; Rosen, Mohs, & Davis, 1984) is commonly implemented, but it is not known precisely where along the spectrum of cognitive dysfunction this subtest yields incremental information beyond what is gained from the standard ADAS-cog, or whether it can improve prediction of functional outcomes. An item response theory approach can analyze this in a psychometrically rigorous way. Seven hundred eighty-eight patients with AD or amnestic complaints or impairment completed a battery including the ADAS-cog and 2 activities of daily living measures. The delayed recall subtest slightly improved the ADAS-cog's measurement precision in the mild range of cognitive dysfunction and increased prediction of instrumental activities of daily living for individuals with subjective memory impairment.

How Do Scores on the ADAS-Cog, MMSE, and CDR-SOB Correspond?

OBJECTIVE: Clinicians and researchers who measure cognitive dysfunction often use the Alzheimer's Disease Assessment Scale--Cognitive Subscale (ADAS-Cog), the Mini-Mental State Examination (MMSE), or the Clinical Dementia Rating scale (CDR-SOB). But, the use of different measures can make it difficult to compare data across patients or studies. What is needed is a simple chart that shows how scores on these three important measures correspond to each other. METHODS: Using data from 1709 participants from the Alzheimer's Disease Neuroimaging Initiative and item response theory-based statistics, we analyzed how scores on each measure, the ADAS-Cog, the MMSE, and the CDR-SOB, correspond. RESULTS: Results indicated multiple inflections in CDR-SOB and ADAS-Cog scores within a given MMSE score, suggesting that the CDR-SOB and ADAS-Cog are more precise in measuring the severity of cognitive dysfunction than the MMSE. CONCLUSIONS: This study shows how scores on these three popular measures of cognitive dysfunction correspond to each other, which is very useful information for both researchers and clinicians.

Using the Alzheimer's Association web site to improve knowledge of Alzheimer's disease in health care providers.

BACKGROUND: The purpose of the current study was to investigate whether an informative Web site is effective at producing higher scores for an individual's knowledge of Alzheimer's disease (AD) relative to those who do not visit a Web site. METHODS: A total of 552 participants completed the study on Amazon's Mechanical Turk; half were randomly assigned to visit alz.org, while a control group did not. Both groups were given the AD Knowledge Scale (ADKS) to assess their knowledge of AD. RESULTS: Participants who visited alz.org scored significantly higher on the ADKS than those in the control group. Participants who were health care workers demonstrated higher scores than others in the experimental condition. Findings indicate that the Alzheimer's Association Web site is effective at producing higher scores for AD knowledge relative to no Web site at all and that it is especially helpful for health care workers compared to those who are not health care workers.

Estimating Premorbid Intelligence among Older Adults: The Utility of the AMNART.

This study examines the utility of the American version of the National Adult Reading Test (AMNART) as a measure of premorbid intelligence for older adults. In a sample of 130 older adults, aged 56 to 104, the AMNART was compared to other tests of premorbid intelligence. The results revealed that AMNART-estimated IQ was significantly higher than other premorbid estimates. Across specific educational groups (i.e., 0-12, 13-16, and 17 or more years of education), AMNART-estimated IQ was inflated relative to all other premorbid estimates. The AMNART also declined as cognitive impairment increased, and there was a significant interaction between aging-related diagnostic group and premorbid estimate. The AMNART may therefore overestimate premorbid ability relative to other premorbid measures, particularly among those with greater cognitive impairment and lower levels of education. These results suggest that the AMNART should be used cautiously among older adults and in conjunction with other estimates of premorbid ability.