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Background: The Mini-mental State Examination (MMSE) is the most widely used cognitive test, both in clinical settings and in epidemiological studies. However, correcting its score for education may create ceiling effects when used for poorly educated people and floor effects for those with higher education. Methods: MMSE and a recent cognitive test, the seven minute screen (7MS), were serially administered to a community sample of Mexican elderly. 7MS test scores were equated to MMSE scores. MMSE-equated 7MS differences indicated ceiling or floor effects. An ordinal logistic regression model was fitted to identify predictors of such effects. Results: Poorly educated persons were more prevalent on the side of MMSE ceiling effects. Concentration (serial-sevens), orientation and memory were the three MMSE subscales showing the strongest relationship to MMSE ceiling effects in the multivariate model. Conclusion: Even when MMSE scores are corrected for educational level they still have ceiling and floor effects. These effects should be considered when interpreting data from longitudinal studies of cognitive decline. When an education-adjusted MMSE test is used to screen for cognitive impairment, additional testing may be required to rule out the possibility of mild cognitive impairment.

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.