Improving the Accuracy and Precision of Cognitive Testing in Mild Dementia

Abstract

The CAMCOG, ADAS-cog, and MMSE, designed to grade global cognitive ability in dementia have inadequate precision and accuracy in distinguishing mild dementia from normal ageing. Adding neuropsychological tests to their scale might improve precision and accuracy in mild dementia. We, therefore, pooled neuropsychological test-batteries from two memory clinics (ns = 135 and 186) with CAMCOG data from a population study and 2 memory clinics (n = 829) and ADAS-cog data from 3 randomized controlled trials (n = 713) to estimate a common dimension of global cognitive ability using Rasch analysis. Item difficulties and individuals' global cognitive ability levels were estimated. Difficulties of 57 items (of 64) could be validly estimated. Neuropsychological tests were more difficult than the CAMCOG, ADAS-cog, and MMSE items. Most neuropsychological tests had difficulties in the ability range of normal ageing to mild dementia. Higher than average ability levels were more precisely measured when neuropsychological tests were added to the MMSE than when these were measured with the MMSE alone. Diagnostic accuracy in mild dementia was consistently better after adding neuropsychological tests to the MMSE. We conclude that extending dementia specific instruments with neuropsychological tests improves measurement precision and accuracy of cognitive impairment in mild dementia.

The Alzheimer’s Disease Assessment Scale–Cognitive Subscale (ADAS-Cog): Modifications and Responsiveness in Pre-Dementia Populations. A Narrative Review

“…Accordingly, 84% of errors made by subjects with NC and 71% of errors made by subjects with MCI occur on Word Recall and Word Recognition [ 18 ]. These two tasks have also been ranked as the most difficult ADAS-Cog-11 tasks by Item Response Theory (IRT) analyses [ 20 ].…”

“…Wouters et al (2012) pooled data from 1863 subjects with a range of cognitive abilities from multiple data sets which each included some or all of the CAMCOG, modified ADAS-Cog (ADAS-Cog-12 plus a concentration task), and MMSE [ 20 ]. Data pooling was performed using “common item equating”, and Rasch measurement models were used to estimate the difficulty of each test item and the cognitive ability of each participant [ 20 ]. The purpose was to locate an underlying dimension of cognitive ability common to all three outcome measures so that their scores could be compared [ 20 ].…”

“…Data pooling was performed using “common item equating”, and Rasch measurement models were used to estimate the difficulty of each test item and the cognitive ability of each participant [ 20 ]. The purpose was to locate an underlying dimension of cognitive ability common to all three outcome measures so that their scores could be compared [ 20 ]. Items showing systematic differences in level of difficulty between data sets, or for which valid estimates of difficulty level could not be obtained, were excluded [ 20 ].…”

Responsiveness of Magnetic Resonance Imaging and Neuropsychological Assessment in Memory Clinic Patients

“…The status of the ADAS and similar scales as the gold standard for pharmacological trials can also be criticized on psychometric grounds [12,[25][26][27][28]. The question arises, therefore, how the comparison with MRI would be if neuropsychological tests with sound psychometric properties were used instead of global scales with intrinsic psychometric shortcomings.…”

Improving the Measurement of Cognitive Ability in Geriatric Patients

“…The ability to detect cognitive decline depends on the adequate measurement of cogniti v e ability even among those who are currently functioning within the normal range. While introducing more items into these tests could improve the measurement of cognitive ability within the higher range, it would also increase the test burden for patients [15] .…”