Age and Ageing Advance Access originally published online on February 28, 2009
Age and Ageing 2009 38(3):277-282; doi:10.1093/ageing/afp004
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Education and trajectories of cognitive decline over 9 years in very old people: methods and risk analysis
1 MRC Biostatistics Unit, Institute of Public Health, Robinson Way, University Forvie Site, Cambridge, CB2 0SR, UK
2 Fulbourn Hospital, Cambridge CB1 5EF, UK
3 Department of Psychiatry, Box 189, Addenbrooke's Hospital, Cambridge, CB2 2QQ, UK
4 Department of Public Health and Primary Care, Institute of Public Health, University of Cambridge, Robinson Way, University Forvie Site, Cambridge, CB2 0SR, UK
5 Cambridge City over 75s Cohort Study group, UK
Address correspondence to: G. Muniz-Terrera. Tel: (+44)-1223-330372; Fax: (+44)-1223-330388. Email: graciela.muniz{at}mrc-bsu.cam.ac.uk
Background: 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.
Methods: 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.
Results: 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
Conclusions: 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.
Keywords: MMSE, education, cognitive decline, longitudinal studies, old age
Received 6 June 2008; accepted in revised form 19 November 2008.