Personne : Talbot, Denis
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Département de médecine sociale et préventive, Faculté de médecine, Université Laval
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- PublicationAccès libreA test for the correct specification of marginal structural models(Wiley, 2019-03-11) Aubé, Karine; Talbot, Denis; Trudel, Xavier; Sall, Alioune; Brisson, ChantalMarginal structural models (MSMs) allow estimating the causal effect of a time‐varying exposure on an outcome in the presence of time‐dependent confounding. The parameters of MSMs can be estimated utilizing an inverse probability of treatment weight estimator under certain assumptions. One of these assumptions is that the proposed causal model relating the outcome to exposure history is correctly specified. However, in practice, the true model is unknown. We propose a test that employs the observed data to attempt validating the assumption that the model is correctly specified. The performance of the proposed test is investigated with a simulation study. We illustrate our approach by estimating the effect of repeated exposure to psychosocial stressors at work on ambulatory blood pressure in a large cohort of white‐collar workers in Québec City, Canada. Code examples in SAS and R are provided to facilitate the implementation of the test.
- PublicationAccès libreImportance of the lipid-related pathways in the association between statins, mortality and cardiovascular disease risk : the multi-ethnic study of atherosclerosis(International Society for Pharmacoepidemiology, 2018-02-06) Talbot, Denis; Delaney, Joseph A. C.; Sandfort, Veit; Herrington, David M.; McClelland, Robyn L.PURPOSE: Estimating how much of the impact of statins on coronary heart diseases (CHD), cardiovascular disease (CVD), and mortality risk is attributable to their effect on low-density lipoprotein cholesterol (LDL), high-density lipoprotein cholesterol (HDL), and triglycerides. METHODS: A semi-parametric g-formula estimator together with data from the Multi-Ethnic Study of Atherosclerosis (a prospective multi-center cohort study) was utilized to perform a mediation analysis. A total of 5280 participants, men and women of various race/ethnicities from multiple sites across the United States, were considered in the current study. RESULTS: The adherence adjusted total relative risk reduction (RRR) estimate (95% confidence interval) of statins on CHD was 14% (-16%, 37%), and the indirect component through LDL was 23% (-4%, 58%). For CVD, the total RRR was 23% (2%, 40%), and the indirect component through LDL was 5% (-13%, 25%). The total RRR of mortality was 18% (-1%, 35%), and the indirect component through LDL was -4% (-17%, 12%). The estimated indirect components through HDL and triglycerides were close to zero with narrow confidence intervals for all 3 outcomes. CONCLUSIONS: The estimated effect of statins on mortality, CVD, and CHD appeared to be independent of their estimated effect on HDL and triglycerides. Our study provides evidence that the preventive effect of statins on CHD could be attributed in large part to their effect on LDL. Our g-formula estimator is a promising approach to elucidate pathways, even if it is hard to make firm conclusions for the LDL pathway on mortality and CVD
- PublicationAccès libreVitamin D status, cognitive decline and incident dementia : the Canadian Study of Health and Aging(Canadian Public Health Association, 2020-02-03) Tourigny, André; Talbot, Denis; Laurin, Danielle; Nafti, Mohamed; Carmichael, Pierre-Hugues; Dodin-Dewailly, Sylvie; Giguère, Yves.; Duchaine, Caroline S.Objective: Vitamin D could prevent cognitive decline because of its neuroprotective, anti-inflammatory and antioxidant properties. This study aimed to evaluate the associations of plasma 25-hydroxyvitamin D (25(OH)D) concentrations with global cognitive function and incident dementia, including Alzheimer’s disease (AD). Methods: The Canadian Study of Health and Aging is a 10-year cohort study of a representative sample of individuals aged 65years or older. A total of 661 subjects initially without dementia with frozen blood samples and follow-up data were included. Global cognitive function was measured using the validated Modified Mini-Mental State (3MS) examination. A consensus diagnosis of all-cause dementia and AD was made between the physician and the neuropsychologist according to published criteria. Cognitive decline for a 5-year increase in age at specific 25(OH)D concentrations was obtained using linear mixedmodels with repeated measures. Hazard ratios of incident dementia and AD were obtained using semi-parametric proportionalhazards models with age as time scale. Results: Over a mean follow-up of 5.4 years, 141 subjects developed dementia of which 100 were AD. Overall, no significant association was found between 25(OH)D and cognitive decline, dementia or AD. Higher 25(OH)D concentrations were associated with an increased risk of dementia and AD in women, but not in men. Conclusion: This study does not support a protective effect of vitamin D status on cognitive function. Further research is needed toclarify the relation by sex.
- PublicationRestreintThe relations between implicit intelligence beliefs, autonomous academic motivation, and school persistence intentions : a mediation model(Kluwer Academic Publishers, 2015-01-21) Talbot, Denis; Renaud Dubé, Andréanne; Guay, Frédéric; Taylor, Geneviève; Koestner, RichardThis study attempts to test a model in which the relation between implicit theories of intelligence and students’ school persistence intentions are mediated by intrinsic, identified, introjected, and external regulations. Six hundred and fifty students from a high school were surveyed. Contrary to expectations, results from ESEM analyses indicated that the four types of regulations do not mediate the relation between implicit theories of intelligence and students’ intentions to persist in school. Rather, results show two direct effects, where an incremental theory of intelligence is associated with greater school persistence intentions, as well as being motivated in an intrinsic manner. In addition, results reveal that academic achievement is related to persistence intentions. No gender differences were observed. This research highlights the importance of promoting students’ incremental intelligence beliefs and intrinsic motivation in order to foster school persistence intentions. Theoretical and practical implications for parents and teachers are discussed.
- PublicationAccès libreA cautionary note concerning the use of stabilized weights in marginal structural models(Wiley Online Library, 2015-03-05) Talbot, Denis; Athertona, Juli; Rossic, Amanda M.; Bacon, Simon L.; Lefebvre, GenevieveMarginal structural models (MSMs) are commonly used to estimate the causal effect of a time-varying treatment in presence of time-dependent confounding. When fitting a MSM to data, the analyst must specify both the structural model for the outcome and the treatment models for the inverse-probability-of-treatment weights. The use of stabilized weights is recommended since they are generally less variable than the standard weights. In this paper, we are concerned with the use of the common stabilized weights when the structural model is specified to only consider partial treatment history, such as the current or most recent treatments. We present various examples of settings where these stabilized weights yield biased inferences while the standard weights do not. These issues are first investigated on the basis of simulated data and subsequently exemplified using data from the Honolulu Heart Program. Unlike common stabilized weights, we find that basic stabilized weights offer some protection against bias in structural models designed to estimate current or most recent treatment effects. Copyright © 2010 John Wiley & Sons, Ltd.
- PublicationAccès libreA graphical perspective of marginal structural models : an application for the estimation of the effect of physical activity on blood pressure(Edward Arnold, 2016-12-29) Talbot, Denis; Rossi, Amanda M.; Bacon, Simon L.; Atherton, Juli; Lefebvre, GenevièveEstimating causal effects requires important prior subject-matter knowledge and, sometimes, sophisticated statistical tools. The latter is especially true when targeting the causal effect of a time-varying exposure in a longitudinal study. Marginal structural models (MSMs) are a relatively new class of causal models which effectively deal with the estimation of the effects of time-varying exposures. MSMs have traditionally been embedded in the counterfactual framework to causal inference. In this paper, we use the causal graph framework to enhance the implementation of MSMs. We illustrate our approach using data from a prospective cohort study, the Honolulu Heart Program. These data consist of 8006 men at baseline. To illustrate our approach, we focused on the estimation of the causal effect of physical activity on blood pressure, which were measured at three time-points. First, a causal graph is built to encompass prior knowledge. This graph is then validated and improved utilizing structural equation models. We estimated the aforementioned causal effect using MSMs for repeated measures and guided the implementation of the models with the causal graph. Employing the causal graph framework, we also show the validity of fitting conditional MSMs for repeated measures in the context implied by our data.
- PublicationAccès libreA descriptive review of variable selection methods in four epidemiologic journals : there is still room for improvement(Kluwer, 2019-06-03) Talbot, Denis; Kubuta Massamba, VictoriaBackground : A review of epidemiological papers conducted in 2009 concluded that several studies employed variable selection methods susceptible to introduce bias and yield inadequate inferences. Many new confounder selection methods have been developed since then. Methods: The goal of the study was to provide an updated descriptive portrait of which variable selection methods are used by epidemiologists for analyzing observational data. Studies published in four major epidemiological journals in 2015 were reviewed. Only articles concerned with a predictive or explicative objective and reporting on the analysis of individual data were included. Method(s) employed for selecting variables were extracted from retained articles. Results : A total of 975 articles were retrieved and 299 met eligibility criteria, 292 of which pursued an explicative objective. Among those, 146 studies (50%) reported using prior knowledge or causal graphs for selecting variables, 34 (12%) used change in effect estimate methods, 26 (9%) used stepwise approaches, 16 (5%) employed univariate analyses, 5 (2%) used various other methods and 107 (37%) did not provide sufficient details to allow classification (more than one method could be employed in a single article). Conclusions : Despite being less frequent than in the previous review, stepwise and univariable analyses, which are susceptible to introduce bias and produce inadequate inferences, were still prevalent. Moreover, 37% studies did not provide sufficient details to assess how variables were selected. We thus believe there is still room for improvement in variable selection methods used by epidemiologists and in their reporting.
- PublicationAccès libreJust how much does it cost? A cost study of chronic pain following cardiac surgery(Dove Medical Press, 2018-11-08) Talbot, Denis; Pagé, Gabrielle M.; Guertin, Jason Robert; Tarride, Jean-Eric; Watt-Watson, Judy; Choinière, ManonObjective: The study objective was to determine use of pain-related health care resources and associated direct and indirect costs over a two-year period in cardiac surgery patients who developed chronic post-surgical pain (CPSP). Methods: This multicentric observational prospective study recruited patients prior to cardiac surgery; these patients completed research assistant-administered questionnaires on pain and psychological characteristics at 6, 12 and 24 months post-operatively. Patients reporting CPSP also completed a one-month pain care record (PCR) (self-report diary) at each follow-up. Data were analyzed using descriptive statistics, multivariable logistic regression models, and generalized linear models with log link and gamma family adjusting for sociodemographic and pain intensity. Results: Out of 1,247 patients, 18%, 13%, and 9% reported experiencing CPSP at 6, 12, and 24 months, respectively. Between 16% and 28% of CPSP patients reported utilizing health care resources for their pain over the follow-up period. Among all CPSP patients, mean monthly pain-related costs were CAN$207 at 6 months and significantly decreased thereafter. More severe pain and greater levels of pain catastrophizing were the most consistent predictors of health care utilization and costs. Discussion: Health care costs associated with early management of CPSP after cardiac surgery seem attributable to a minority of patients and decrease over time for most of them. Results are novel in that they document for the first time the economic burden of CPSP in this population of patients. Longer follow-up time that would capture severe cases of CPSP as well as examination of costs associated with other surgical populations are warranted. Summary: Economic burden of chronic post-surgical pain may be substantial but few patients utilize resources. Health utilization and costs are associated with pain and psychological characteristics.
- PublicationAccès libreEstimation de la variance et construction d'intervalles de confiance pour le ratio standardisé de mortalité avec application à l'évaluation d'un programme de dépistage du cancer(2010) Talbot, Denis; Duchesne, Thierry; Brisson, JacquesL'effet d'un programme de dépistage de cancer peut être évalué par le biais d'un ratio standardisé de mortalité (SMR). Dans ce mémoire, nous proposons un estimateur de la variance du dénominateur du SMR, c'est-à-dire du nombre de décès attendus, dans le cas où ce dernier est calculé selon la méthode de Sasieni. Nous donnons d'abord une expression générale pour la variance, puis développons des cas particuliers où des estimateurs spécifiques de l'incidence de la maladie et de son temps de survie sont utilisés. Nous montrons comment ce nouvel estimateur de la variance peut être utilisé dans la construction d'intervalles de confiance pour le SMR. Nous étudions la couverture de différents types d'intervalles de confiance par le biais de simulations et montrons que les intervalles utilisant l'estimateur de variance proposé disposent des meilleures propriétés. Nous appliquons la méthode suggérée sur les données du Programme québécois de dépistage du cancer du sein.