Examining the influence of drop-outs in a follow-up of maintained opiate users
Drug and Alcohol Dependence. 2005-09-01; 79(3): 303-310
DOI: 10.1016/j.drugalcdep.2005.01.021
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1. Drug Alcohol Depend. 2005 Sep 1;79(3):303-10. Epub 2005 Mar 31.
Examining the influence of drop-outs in a follow-up of maintained opiate users.
Encrenaz G(1), Rondeau V, Messiah A, Auriacombe M.
Author information:
(1)Laboratoire de Psychiatrie and Jeune Equipe 2358, Bordeaux, France.
INTRODUCTION: In most longitudinal studies of problem opiate users, drop-outs are
frequent, but not taken into account. However, missing data can induce important
bias in parameters estimates.
OBJECTIVE: The aim of this study was to examine the influence of drop-outs in the
statistical analysis of a follow-up of opiate users in maintenance treatment.
METHODS: Participants were 519 patients who had sought maintenance treatment
between 1994 and 2001. Drug use was studied using the drug composite score of the
Addiction Severity Index. A classical data analysis (linear mixed effects model
for repeated measurements) was compared with a selection model, which consists,
in this case, of a joint modelling of the score and of the drop-out probability
in order to reduce bias induced by drop-outs.
RESULTS: At 18 months, 38% of the patients were available for evaluation.
Drop-outs were associated with low drug use and were informative. Each model
showed that the score decreased over time and that it was associated with
psychiatric problems. Unlike the classical method, the joint model showed no
significant association between the score and age or treatment setting.
CONCLUSIONS: These results show the importance of accounting for informative
drop-outs in data analysis before drawing conclusions from such studies.
DOI: 10.1016/j.drugalcdep.2005.01.021
PMID: 16102374 [Indexed for MEDLINE]