Intérêt de la détection et de la prise en compte d’une surdispersion dans un modèle de Poisson : illustration à partir d’un exemple

BackgroundResearchers often use the Poisson regression model to analyze count data. Overdispersion can occur when a Poisson regression model is used, resulting in an underestimation of variance of the regression model parameters. Our objective was to take overdispersion into account and assess its impact with an illustration based on the data of a study investigating the relationship between use of the Internet to seek health information and number of primary care consultations.MethodsThree methods, overdispersed Poisson, a robust estimator, and negative binomial regression, were performed to take overdispersion into account in explaining variation in the number (Y) of primary care consultations. We tested overdispersion in the Poisson regression model using the ratio of the sum of Pearson residuals over the number of degrees of freedom (χ²/df). We then fitted the three models and compared parameter estimation to the estimations given by Poisson regression model.ResultsVariance of the number of primary care consultations (Var[Y] = 21.03) was greater than the mean (E[Y] = 5.93) and the χ²/df ratio was 3.26, which confirmed overdispersion. Standard errors of the parameters varied greatly between the Poisson regression model and the three other regression models. Interpretation of estimates from two variables (using the Internet to seek health information and single parent family) would have changed according to the model retained, with significant levels of 0.06 and 0.002 (Poisson), 0.29 and 0.09 (overdispersed Poisson), 0.29 and 0.13 (use of a robust estimator) and 0.45 and 0.13 (negative binomial) respectively.ConclusionDifferent methods exist to solve the problem of underestimating variance in the Poisson regression model when overdispersion is present. The negative binomial regression model seems to be particularly accurate because of its theorical distribution ; in addition this regression is easy to perform with ordinary statistical software packages.     

Investigation et gestion d’un foyer de saturnisme infantile dans un quartier de la commune du Port, Île de la Réunion

BackgroundA national survey conducted in 2008–2009 by the French Institute for Public Health Surveillance for detection of lead impact in childhood identified a high blood lead level in a young boy living in the town of “Le Port”, Reunion Island. Previously, cases of lead-poisoning on the island had been exceptional; only a dozen cases were reported in the 1980s in adults, related to the use of lead-containing instruments for food preparations.MethodsThe family of the index case was invited to participate in screening tests and an environmental investigation was conducted using a standardized questionnaire. Screening was then broadened to the neighborhood of the index case and samples of soil outside the home and in the immediate vicinity were taken. The environmental survey was then extended with soil samples taken from the entire geographical area. Information was then provided to local inhabitants (87 families and 287 people) in order to encourage lead blood testing for all children under six years and all pregnant women living in the area.ResultsThe index case lived in the neighborhood of “The Oasis”, a shantytown of Le Port. The results of soil analysis revealed heterogeneous pollution of superficial soils by lead throughout the area of the shantytown, the highest level recorded (5200 mg/kg) reached more than 300 times the background level of the natural soils of the island. The screening identified 76 cases of childhood lead-poisoning (blood lead level greater or equal to 100 μg/L) among 148 samples (51%). All cases of blood poisoning involved children under the age of 15 years. The median age of children with a positive test was 5.6 years; the median blood lead level was 196 μg/L [102–392 μg/L].ConclusionThe main hypothesis to explain the contamination of the soil in the area of the shantytown is the presence of waste deposits (car batteries) and diffuse activities of metal recovery. The authorities managed to remove all the families from the environmental exposure to lead by rapidly ensuring rehousing outside the contaminated area.     

La ghréline et ses analogues dans le traitement de l’anorexie et de la cachexie cancéreuse

Ghrelin is one of the appetite-stimulating neuro-hormones. It also participates in regulation of energy expenditure and muscle anabolism. It intervenes in the digestive motricity. Its secretion by the stomach and its action on hypothalamus could be altered by pro-inflammatory cytokines during cancer cachexia. Ghrelin supplementation in animal models of cancer cachexia partly reverses these phenomena, and improves energy intake and muscle mass. This beneficial effect is not found in humans. Anamorelin, a ghrelin analogue, which can be administered orally, has been tested in cachectic patients. Anamorelin improves muscle mass and appetite but has no effect on muscle function and survival. The combination of anamorelin, dietary counseling and physical activity could be more effective on functional status and quality of life. Multimodal and early management including ghrelin or one of its analogues must be evaluated in large randomized controlled trials.     

Régulation de la balance énergetique : ajustement de l’apport alimentaire à la dépense énergétique

Studies investigating the effect of exercise on body composition, as well as studies investigating the effect of exercise on ad libitum energy intake, provide insight into the association between exercise and energy balance. Reduced levels of physical activity does not exhibit a compensatory reduction of energy intake, and lead to a positive energy balance, most of which is stored as body fat. By contrast, high intensity exercise performed on regular basis increases energy intake in highly trained subjects and lean individuals. Obese untrained persons commonly do not change energy intake when exposed to exercise training. It can be concluded that regular high level of physical activity increases food intake secondary to excess body fat storage utilization, and thus serves as an effective strategy for obesity reduction. The physical activity recommendations for clinically significant weight loss are discussed herein.