title: The association between different cognitive domains and age in a multi-centre study of middle-aged and older European men.
abstract: OBJECTIVE
  We determined levels of cognitive functioning in community dwelling men aged 40-79 (n = 3265) from eight European centres and investigated to what extent cognitive performance varied between centres, the association between different cognitive domains and age, educational level, co-morbidity and lifestyle factors and the respective contributions of centre and individual factors to cognitive performance.
  
  
  METHODS
  Cognitive domains assessed were visuo-constructional ability and visual memory (Rey-Osterrieth Complex Figure test, ROCF), topographical memory (Camden Topographical Recognition Memory test, CTRM) and processing speed (Digit-Symbol Substitution test, DSST).
  
  
  RESULTS
  There were significant between-centre differences in all four cognitive test scores. Using multilevel linear regression analysis (MLRA), age, education, depression, physical performance and smoking were independent predictors of cognitive function and these variables explained 10-13% of the variation in cognitive scores between centres and 17-36% of the variation in scores between individuals within centres.
  
  
  CONCLUSIONS
  Our data suggest that although a proportion of the variance in cognitive function among European men is explained by individual level differences, a significant proportion is due to contextual phenomenon. Such contextual factors need to be considered when analysing multi-centre data and European men should not be treated as homogeneous when assessing cognitive performance using existing instruments.
authors.affiliation: ARC Epidemiology Unit, The University of Manchester, Manchester, UK. david.m.lee@manchester.ac.uk
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