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Updated: May 17, 2026

A Naturalistic Setup for Presenting Real People and Live Actions in Experimental Psychology and Cognitive Neuroscience Studies
Published on: August 4, 2023
Analysing cognitive test data: Distributions and non-parametric random effects
Graciela Muniz-Terrera1, Ardo van den Hout2, R A Rigby3
1MRC Unit for Lifelong Health and Aging, London, UK g.muniz@nshd.mrc.ac.uk.
Abstract:
An important assumption in many linear mixed models is that the conditional distribution of the response variable is normal. This assumption is violated when the models are fitted to an outcome variable that counts the number of correctly answered questions in a questionnaire. Examples include investigations of cognitive decline where models are fitted to Mini Mental State Examination scores, the most widely used test to measure global cognition. Mini Mental State Examination scores take integer values in the 0-30 range, and its distribution has strong ceiling and floor effects. This article explores alternative distributions for the outcome variable in mixed models fitted to mini mental state examination scores from a longitudinal study of ageing. Model fit improved when a beta-binomial distribution was chosen as the distribution for the response variable.
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