CC75C group. Education and trajectories of cognitive decline over 9 years in very old people: methods and risk analysis

MRC Biostatistics Unit, Institute of Public Health, Robinson Way, University Forvie Site, Cambridge, CB2 0SR, UK.
Age and Ageing (Impact Factor: 3.64). 03/2009; 38(3):277-82. DOI: 10.1093/ageing/afp004
Source: PubMed


the investigation of cognitive decline in the older population has been hampered by analytical considerations. Most studies of older people over prolonged periods suffer from loss to follow-up, yet this has seldom been investigated fully to date. Such considerations limit our understanding of how basic variables such as education can affect cognitive trajectories.
we examined cognitive trajectories in a population-based cohort study in Cambridge, UK, of people aged 75 and over in whom multiple interviews were conducted over time. Cognitive function was assessed using the Mini-Mental State Examination (MMSE). Socio-demographic variables were measured, including educational level and social class. An age-based quadratic latent growth model was fitted to cognitive scores. The effect of socio-demographic variables was examined on all latent variables and the probability of death and dropout.
at baseline, age, education, social class and mobility were associated with cognitive performance. Education and social class were not related to decline or its rate of change. In contrast, poor mobility was associated with lower cognitive performance, increased cognitive decline and increased rate of change of cognitive decline. Gender, age, mobility and cognitive ability predicted death and dropout
contrary to much of the current literature, education was not related to rate of cognitive decline or change in this rate as measured by MMSE. Higher levels of education do not appear to protect against cognitive decline, though if the MMSE is used in the diagnostic process, individuals with less education may be diagnosed as having dementia somewhat earlier.

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Available from: Tom Dening, Apr 17, 2014
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    • "It is possible that improvements in MMSE scores may be due to learning effects [28] ; however, the testretest reliability of the MMSE ranged from 0.83 to 0.95 for an interval as short as 1 day across various populations [29]. In addition, while the scores improved, a 1-point change in MMSE scores may not be clinically relevant; wide standard deviations in MMSE scores in the included studies consistent with findings in Alzheimer's Disease Neuroimaging Initiative cohort [30] and other reports [31, 32] suggest that differences between clinical changes and possible effects of confounding variables such as sex, education [32], and functional status [31] may be difficult to interpret. The MMSE has also been suggested to be insufficient in probing executive function and may lack sensitivity in detecting subtle memory impairment [27]. "
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    • "However, there are still some mixed findings, particularly for models that examine education and cognitive change [8–12], which may stem from methodological issues. For example, it is rare for longitudinal analyses of cognitive decline in the older population to account for death and dropout, measurement error of the cognitive phenotype, ceiling and floor effects in the cognitive test [13], and the possibility of cognitive recovery, especially from the mild cognitive impairment state [14]. "
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    • "We did not explicitly model the risk of dropout or death in this study. A recent study concerning education and cognitive decline [44] suggests this modelling approach may be a worthy avenue for future investigation in this area. A final point is that the MMSE is a crude screening tool for dementia. "
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