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Effect of Different Impairment Criteria on Prevalence of “Objective” Mild Cognitive Impairment in a Community Sample

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Objectives

Objective cognitive impairment determined by neuropsychological test performance is a core criterion for the diagnosis of mild cognitive impairment (MCI), yet no consensus has been reached on how this criterion should be operationalized. The aims of this study were to investigate the effect of varying the criteria used to determine cognitive impairment (CI) on prevalence and case definition and to examine comparability of different criteria.

Design

Cross-sectional study.

Setting

Sydney Memory and Ageing Study, Australia.

Participants

Nine hundred eighty-seven nondemented community-dwelling adults aged 70–90 years were enrolled in this study.

Measurements

Participants received a comprehensive neuropsychological test battery measuring four cognitive domains. They were classified as normal or cognitively impaired by applying two types of “impairment” rule that varied the statistical threshold for impairment and the criteria used to determine impairment for each cognitive domain. Prevalence of four MCI cognitive subtypes was determined according to nine different criteria and two types of normative data. Rates of CI were compared in persons of English-speaking and non-English-speaking backgrounds (NESB).

Results

Prevalence of CI ranged from 4 to 70% depending on the impairment criteria used. Agreement between different criteria was poor to moderate. This lack of consistency had greatest impact on MCI subtype classifications with many being reclassified as “normal” or into a different subtype when stringency of the criteria was increased or decreased. Higher rates of impairment were found in persons of NESB across all cognitive domains.

Conclusions

The prevalence of CI was strongly affected by the choice of neuropsychological assessment parameters. Guidelines for operationalizing CI are required.

Section snippets

Participants

Commencing in 2005, participants aged 70–90 years were recruited randomly from the eastern suburbs of Sydney, Australia, using the electoral roll for the Sydney Memory and Ageing Study, a longitudinal study of nondemented older individuals living in the community. All were fluent in English and were judged to have sufficient proficiency in English to complete a psychometric assessment, and the majority (93.6%) had a suitable informant to provide collateral information. Individuals were excluded

Description of the Sample

As can be seen from Table 1, the NESB group was slightly older, had lower scores on the standard MMSE but higher scores on the adjusted MMSE. There were no group differences in instrumental activities of daily living.37

Examination of the ethnic and language characteristics of the NESB sample revealed that 85% of the participants were of European background and had lived in Australia for most of their adult life (mean = 51.43 years, SD = 11.81). The main language spoken at home was English for

DISCUSSION

This study demonstrates that the prevalence of CI is strongly affected by the choice of psychometric parameters for defining “objective CI,” with the agreement between various criteria being poor to moderate. As would be expected, a simple “Impaired” versus “Normal” dichotomy is more stable in the face of changing criteria than the subtypes of CI. The potential for misclassification of CI is greater in persons of NESB using normative data derived from mainly native English speakers as they show

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    The authors thank all the participants and the research team of the Sydney Memory and Ageing Study.

    This work was supported by the Australian National Health and Medical Research Council Program Grant (350833) and Capacity Building Grant (568940).

    An earlier version of this work was presented at the International Conference on Alzheimer's Disease July 11–16, 2009, Vienna.

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    Copyright © 2010 American Association for Geriatric Psychiatry. Published by Elsevier Inc. All rights reserved.