title: Mixed models for longitudinal left-censored repeated measures.
abstract: Longitudinal studies could be complicated by left-censored repeated measures. For example, in Human Immunodeficiency Virus infection, there is a detection limit of the assay used to quantify the plasma viral load. Simple imputation of the limit of the detection or of half of this limit for left-censored measures biases estimations and their standard errors. In this paper, we review two likelihood-based methods proposed to handle left-censoring of the outcome in linear mixed model. We show how to fit these models using SAS Proc NLMIXED and we compare this tool with other programs. Indications and limitations of the programs are discussed and an example in the field of HIV infection is shown.
authors.affiliation: ISPED, INSERM E0338 Biostatistics, Université Victor Segalen Bordeaux II, 146, Rue Léo Saignat 33076, Bordeaux Cedex, France. rodolphe.thiebaut@isped.u-bordeaux2.fr
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Thiébaut
authors.forename: Hélène
authors.initials: H
authors.lastname: Jacqmin-Gadda
mesh_terms: D015658:HIV Infections / Q000821:virology; D006801:Humans; D016013:Likelihood Functions; D008137:Longitudinal Studies; D015233:Models, Statistical; D019562:Viral Load