title: A nonlinear model with latent process for cognitive evolution using multivariate longitudinal data.
abstract: Cognition is not directly measurable. It is assessed using psychometric tests, which can be viewed as quantitative measures of cognition with error. The aim of this article is to propose a model to describe the evolution in continuous time of unobserved cognition in the elderly and assess the impact of covariates directly on it. The latent cognitive process is defined using a linear mixed model including a Brownian motion and time-dependent covariates. The observed psychometric tests are considered as the results of parameterized nonlinear transformations of the latent cognitive process at discrete occasions. Estimation of the parameters contained both in the transformations and in the linear mixed model is achieved by maximizing the observed likelihood and graphical methods are performed to assess the goodness of fit of the model. The method is applied to data from PAQUID, a French prospective cohort study of ageing.
authors.affiliation: INSERM E0338, Université de Bordeaux 2, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France. Cecile.Proust@isped.u-bordeaux2.fr
authors.forename: Cécile
authors.initials: C
authors.lastname: Proust
authors.forename: Hélène
authors.initials: H
authors.lastname: Jacqmin-Gadda
authors.forename: Jeremy M G
authors.initials: JM
authors.lastname: Taylor
authors.forename: Julien
authors.initials: J
authors.lastname: Ganiayre
authors.forename: Daniel
authors.initials: D
authors.lastname: Commenges
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000523:psychology*; D001699:Biometry; D003071:Cognition; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D005602:France; D006801:Humans; D016013:Likelihood Functions; D016014:Linear Models; D008137:Longitudinal Studies; D008960:Models, Psychological; D015999:Multivariate Analysis; D017711:Nonlinear Dynamics; D011446:Prospective Studies; D011594:Psychometrics