Considering the base rates of low performance in cognitively healthy older adults improves the accuracy to identify neurocognitive impairment with the Consortium to Establish a Registry for Alzheimer’s Disease-Neuropsychological Assessment Battery (CERAD-NAB)
Panagiota Mistridis
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Simone C. Egli
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Grant L. Iverson
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Manfred Berres
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Klaus Willmes
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Kathleen A. WelshBohmer
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Andreas U. Monsch
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G. L. Iverson Department of Physical Medicine and Rehabilitation, Harvard Medical School
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Boston, MA 02114
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USA
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P. Mistridis S. C. Egli A. U. Monsch Department of Psychology, University of Basel
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Missionsstrasse 60/62, 4055 Basel
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Switzerland
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P. Mistridis S. C. Egli A. U. Monsch (
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) Memory Clinic, Felix Platter Hospital, University Center for Medicine of Aging Basel
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Schanzenstrasse 55, 4031 Basel
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Switzerland
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K. A. Welsh-Bohmer Joseph and Kathleen Bryan Alzheimer's Disease Center, Duke University
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2200W Main Street, Suite A200, Durham, NC 27705
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USA
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K. Willmes Section Neuropsychology, Department of Neurology, RWTH Aachen University
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Pauwelsstrae 30, 52074 Aachen
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Germany
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M. Berres Department of Mathematics and Technology, University of Applied Sciences Koblenz
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Joseph-Rovan-Allee 2, 53424 Remagen
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Germany
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G. L. Iverson Red Sox Foundation and Massachusetts General Hospital Home Base Program
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Boston, MA 02114
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USA
It is common for some healthy older adults to obtain low test scores when a battery of neuropsychological tests is administered, which increases the risk of the clinician misdiagnosing cognitive impairment. Thus, base rates of healthy individuals' low scores are required to more accurately interpret neuropsychological results. At present, this information is not available for the German version of the Consortium to Establish a Registry for Alzheimer's Disease-Neuropsychological Assessment Battery (CERAD-NAB), a frequently used battery in the USA and in German-speaking Europe. This study aimed to determine the base rates of low scores for the CERAD-NAB and to tabulate a summary figure of cut-off scores and numbers of low scores to aid in clinical decision making. The base rates of low scores on the ten German CERAD-NAB subscores were calculated from the German CERAD-NAB normative sample (N = 1,081) using six different cut-off scores (i.e., 1st, 2.5th, 7th, 10th, 16th, and 25th percentile). Results indicate that high percentages of one or more abnormal scores were obtained, irrespective of the cut-off criterion. For example, 60.6 % of the normative sample obtained one or more scores at or below the 10th percentile. These findings illustrate the importance of considering the prevalence of low scores in healthy individuals. The summary figure of CERAD-NAB base rates is an important supplement for test interpretation and can be used to improve the diagnostic accuracy of neurocognitive disorders.
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When administered a battery of neuropsychological tests,
some healthy older adults obtain low scores (e.g., [16]).
Low test scores, especially low memory scores, obtained by
healthy older adults might be interpreted as an indication of
cognitive deterioration and lead to a false-positive
diagnosis of mild cognitive impairment (MCI). Thus, to evaluate
test results accurately and safeguard against
misinterpretation of abnormal test performance, knowledge about base
rates of low scores in healthy older adults compared to true
pathological performance is of critical importance.
Cognitive deficits, particularly in episodic memory,
represent a hallmark of Alzheimers disease (AD) dementia
and are known to be detectable in prodromal stages, such
as MCI [79]. However, given that healthy older adults
may also show a gradual but clinically insignificant
cognitive decline over time [10, 11], these cognitive changes
may be very subtle, such that in clinical practice detecting
true cognitive impairment remains challenging [8]. Thus, to
obtain an accurate understanding of an individuals
cognitive functioning for a reliable and valid diagnosis, it is very
important to differentiate normal changes with cognitive
aging from cognitive changes that go beyond normal aging.
At present, however, no universally accepted and
empirically validated psychometric criteria exist to define
cognitive impairment [12, 13]. Cognitive deterioration is broadly
defined in clinical practice, and different cut-off scores are
used to define impairment. Thus, when assessing cognitive
impairment, some methodological issues have to be
considered. When administering only one neuropsychological
test, the number of individuals being within the lower tail
of the Gaussian distribution will depend on the chosen
cutoff score (e.g., when using the 7th percentile as the
critical cut-off score, by definition, 7 % of cognitively healthy
individuals would be erroneously classified as impaired).
However, clinicians usually do not rely on a single test
score, but on the patients performance on multiple tests
when assessing cognition. The prevalence of low scores
will then be considerably higher when the number of tests
administered increases, compared to single test
interpretation [1, 12]. Additionally, tests (...truncated)