title: Adult Lifespan Cognitive Variability in the Cross-Sectional Cam-CAN Cohort.
abstract: This study examines variability across the age span in cognitive performance in a cross-sectional, population-based, adult lifespan cohort from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN) study (n = 2680). A key question we highlight is whether using measures that are designed to detect age-related cognitive pathology may not be sensitive to, or reflective of, individual variability among younger adults. We present three issues that contribute to the debate for and against age-related increases in variability. Firstly, the need to formally define measures of central tendency and measures of variability. Secondly, in addition to the commonly addressed location-confounding (adjusting for covariates) there may exist changes in measures of variability due to confounder sub-groups. Finally, that increases in spread may be a result of floor or ceiling effects; where the measure is not sensitive enough at all ages. From the Cam-CAN study, a large population-based dataset, we demonstrate the existence of variability-confounding for the immediate episodic memory task; and show that increasing variance with age in our general cognitive measures is driven by a ceiling effect in younger age groups.
authors.affiliation: Department of Public Health and Primary Care, Cambridge Institute of Public Health, Univeristy of Cambridge, Cambridge CB2-0SR, UK. ep382@medschl.cam.ac.uk.
authors.forename: Emma
authors.initials: E
authors.lastname: Green
authors.affiliation: Centre for Speech, Language and the Brain, Department of Psychology, University of Cambridge, Downing Street, Cambridge CB2-3EB, UK. mshafto@csl.psychol.cam.ac.uk.
authors.forename: Meredith A
authors.initials: MA
authors.lastname: Shafto
authors.affiliation: MRC Biostatistics Unit, Cambridge CB2-0SR, UK. fiona.matthews@mrc-bsu.cam.ac.uk.|Institute of Health and Society, Newcastle University, Newcastle NE4-5PL, UK. fiona.matthews@mrc-bsu.cam.ac.uk.
authors.forename: Fiona E
authors.initials: FE
authors.lastname: Matthews
authors.affiliation: MRC Biostatistics Unit, Cambridge CB2-0SR, UK. simon.white@mrc-bsu.cam.ac.uk.
authors.forename: Simon R
authors.initials: SR
authors.lastname: White
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003071:Cognition / Q000502:physiology*; D003072:Cognition Disorders / Q000175:diagnosis* / Q000503:physiopathology; D000066492:Cognitive Aging; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D011581:Psychological Tests; D055815:Young Adult
keywords: MMSE; adult lifespan; ceiling effects; cognitive variability; episodic memory; heterogeneity; variance confounders; verbal fluency