Le rôle des attributions dans la relation entre l'environnement socio-professionnel et le niveau habituel d'estime de soi : le cas des serveuses de bar

Québec Université Laval, Bibliothèque 201

3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Inhibitors and the Risk of Cancer

Background During the past 15 years there has been an exponential increase in the number of prescriptions for lipid-lowering drugs. Uncertainties remain about the long-term impact of these medications on cancer, which is particularly bothersome given that the duration of these treatments may extend for several decades.\ud Objective To explore the association between 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors and cancer incidence.\ud Methods Using the administrative health databases of the Régie de l'Assurance-Maladie du Québec we performed a nested case-control study. We selected a cohort of 6721 beneficiaries of the health care plan of Quebec who were free of cancer for at least 1 year at cohort entry, 65 years and older, and treated with lipid-modifying agents. Cohort members were selected between 1988 and 1994 and were followed up for a median period of 2.7 years. From the cohort, 542 cases of first malignant neoplasm were identified, and 5420 controls were randomly selected. Users of HMG-CoA reductase inhibitors were compared with users of bile acid–binding resins as to their risk of cancer. Specific cancer sites were also considered.\ud Results Users of HMG-CoA reductase inhibitors were found to be 28% less likely than users of bile acid–binding resins to be diagnosed as having any cancer (rate ratio, 0.72; 95% confidence interval, 0.57-0.92). All specific cancer sites under study were found to be not or inversely associated with the use of HMG-CoA reductase inhibitors.\ud Conclusion The results of our study provide some degree of reassurance about the safety of HMG-CoA reductase inhibitors

Understanding and diagnosing the potential for bias when using machine learning methods with doubly robust causal estimators

Data-adaptive methods have been proposed to estimate nuisance parameters when using doubly robust semiparametric methods for estimating marginal causal effects. However, in the presence of near practical positivity violations, these methods can produce a separation of the two exposure groups in terms of propensity score densities which can lead to biased estimates of the treatment effect. To motivate the problem, we evaluated the Targeted Minimum Loss-based Estimation procedure using a simulation scenario to estimate the average treatment effect. We highlight the divergence in estimates obtained when using parametric and data-adaptive methods to estimate the propensity score. We then adapted an existing diagnostic tool based on a bootstrap resampling of the subjects and simulation of the outcome data in order to show that the estimation using data-adaptive methods for the propensity score in this study may lead to large bias and poor coverage. The adapted bootstrap procedure is able to identify this instability and can be used as a diagnostic tool

Impact of discretization of the timeline for longitudinal causal inference methods

In longitudinal settings, causal inference methods usually rely on a discretization of the patient timeline that may not reflect the underlying data generation process. This paper investigates the estimation of causal parameters under discretized data. It presents the implicit assumptions practitioners make but do not acknowledge when discretizing data to assess longitudinal causal parameters. We illustrate that differences in point estimates under different discretizations are due to the data coarsening resulting in both a modified definition of the parameter of interest and loss of information about time-dependent confounders. We further investigate several tools to advise analysts in selecting a timeline discretization for use with pooled Longitudinal Targeted Maximum Likelihood Estimation for the estimation of the parameters of a marginal structural model. We use a simulation study to empirically evaluate bias at different discretizations and assess the use of the cross-validated variance as a measure of data support to select a discretization under a chosen data coarsening mechanism. We then apply our approach to a study on the relative effect of alternative asthma treatments during pregnancy on pregnancy duration. The results of the simulation study illustrate how coarsening changes the target parameter of interest as well as how it may create bias due to a lack of appropriate control for time-dependent confounders. We also observe evidence that the cross-validated variance acts well as a measure of support in the data, by being minimized at finer discretizations as the sample size increases

Relationship between Adherence Level to Statins, Clinical Issues and Health-Care Costs in Real-Life Clinical Setting

AbstractObjectiveStatins have been shown to reduce the risk of major cardiovascular disease. We recognize that there is a major gap between the use of statins in actual practice and treatment guidelines for dyslipidemia. Low adherence to statins may have a significant impact on clinical issues and health-care costs. The objective is to evaluate the impact of low adherence to statins on clinical issues and direct health-care costs.MethodsA cohort of 55,134 patients newly treated with statins was reconstructed from the Régie de l'Assurance Maladie du Québec and Med-Echo databases. Subjects included were aged between 45 and 85, initially free of cardiovascular disease, newly treated with statins between 1999 and 2002, and followed-up for a minimum of 3 years. Adherence to statins was measured in terms of the proportion of days' supply of medication dispensed over a defined period, and categorized as ≥80% or <80%. The adjusted odds ratio (OR) of cardiovascular events between the two adherence groups was estimated using a polytomous logistic analysis. The mean costs of direct health-care services were evaluated. A two-part model was applied for hospitalization costs.ResultsThe mean high adherence level to statins was around to 96% during follow-up; and this value was at 42% for the low adherence level. The patients with low adherence to statins were more likely to have coronary artery disease (OR 1.07; 95% confidence interval [CI], 1.01–1.13), cerebrovascular disease (OR 1.13; 95% CI 1.03–1.25), and chronic heart failure within 3-year period of follow-up (OR 1.13; 95% CI 1.01–1.26). Low adherence to statins was also associated with an increased risk of hospitalization by 4% (OR 1.04; 95% CI 1.01–1.09). Among patients who were hospitalized, low adherence to statins was significantly associated with increase of hospitalization costs by approximately $1060/patient for a 3-year period.ConclusionLow adherence to statins was correlated with a higher risk of cardiovascular disease, hospitalization rate, and hospitalization costs. An increased level of adherence to statins agents should provide a better health status for individuals and a net economic gain

Association between gestational weight gain, gestational diabetes risk, and obstetric outcomes: A randomized controlled trial post hoc analysis

Excess gestational weight gain (GWG) is associated with the development of gestational diabetes mellitus (GDM). Lifestyle trials have not achieved much GWG limitation, and have largely failed to prevent GDM. We compared the effect of substantial GWG limitation on maternal GDM risk. Pregnant women with a body mass index (BMI) ≥29 kg/m2 \u3c20 weeks gestation without GDM (n = 436) were randomized, in a multicenter trial, to usual care (UC), healthy eating (HE), physical activity (PA), or HE and PA lifestyle interventions. GWG over the median was associated with higher homeostasis model assessment insulin resistance (HOMA-IR) and insulin secretion (Stumvoll phases 1 and 2), a higher fasting plasma glucose (FPG) at 24–28 weeks (4.66 ± 0.43 vs. 4.61 ± 0.40 mmol/L, p \u3c 0.01), and a higher rate of caesarean section (38% vs. 27% p \u3c 0.05). The GWG over the median at 35–37 weeks was associated with a higher rate of macrosomia (25% vs. 16%, p \u3c 0.05). A post hoc comparison among women from the five sites with a GWG difference \u3e3 kg showed no significance difference in glycaemia or insulin resistance between HE and PA, and UC. We conclude that preventing even substantial increases in GWG after the first trimester has little effect on maternal glycaemia. We recommend randomized controlled trials of effective lifestyle interventions, starting in or before the first trimester

Seabird Modulations of Isotopic Nitrogen on Islands

The transport of nutrients by migratory animals across ecosystem boundaries can significantly enrich recipient food webs, thereby shaping the ecosystems’ structure and function. To illustrate the potential role of islands in enabling the transfer of matter across ecosystem boundaries to be gauged, we investigated the influence of seabirds on nitrogen input on islands. Basing our study on four widely differing islands in terms of their biogeography and ecological characteristics, sampled at different spatial and temporal intervals, we analyzed the nitrogen isotopic values of the main terrestrial ecosystem compartments (vascular plants, arthropods, lizards and rodents) and their relationship to seabird values. For each island, the isotopic values of the ecosystem were driven by those of seabirds, which ultimately corresponded to changes in their marine prey. First, terrestrial compartments sampled within seabird colonies were the most enriched in δ15N compared with those collected at various distances outside colonies. Second, isotopic values of the whole terrestrial ecosystems changed over time, reflecting the values of seabirds and their prey, showing a fast turnover throughout the ecosystems. Our results demonstrate that seabird-derived nutrients not only spread across the terrestrial ecosystems and trophic webs, but also modulate their isotopic values locally and temporally on these islands. The wealth of experimental possibilities in insular ecosystems justifies greater use of these model systems to further our understanding of the modalities of trans-boundary nutrient transfers

Observational studies of drug effectiveness in asthma : time-related issues

This thesis relates to the study of drug effectiveness using observational designs. First, we investigate the ability of inhaled corticosteroids, an anti-asthma medication, in preventing hospitalization for asthma. We then address methodological issues related to temporal dimensions of drug exposure and to the estimation of time-dependent rate ratios in case-control studies. To examine these questions, a cohort of 19,168 newly treated asthmatics was selected from the computerized databases of Saskatchewan Health.Using a sub-cohort of 2,059 patients hospitalized for asthma, we found that regular users of inhaled corticosteroids were about 40 percent less likely to be readmitted to hospital for asthma than nonusers of these medications, and this after only 15 days of therapy. The beneficial effects lasted up to six months and waned thereafter. Using a case-control sample from the entire cohort, we found that therapy with inhaled corticosteroids, initiated early after the onset of symptoms of asthma, was more effective than theophylline in preventing the first hospitalization for asthma. When compared with anti-allergic agents, early treatment with inhaled corticosteroids was not found to significantly reduce the risk of asthma hospitalization, however.Finally, we showed that the common use of exposure time-windows defined solely in terms of the outcome produces biased estimates of rate ratios that vary over time. Application of principles based on time-related dimensions of exposure provides, however, valid case-control estimates of time-dependent rate ratios.In conclusion, we were able to show that regular use of inhaled corticosteroids is highly effective in preventing asthma hospitalizations. We also showed the importance of defining the exposure in terms of both the onset of therapy and the time of the outcome for the valid estimation of time-dependent rate ratios in case-control studies