A graphical perspective of marginal structural models: An application for the estimation of the effect of physical activity on blood pressure.

Estimating 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 are a relatively new class of causal models that effectively deal with the estimation of the effects of time-varying exposures.

A cautionary note concerning the use of stabilized weights in marginal structural models.

Marginal structural models are commonly used to estimate the causal effect of a time-varying treatment in presence of time-dependent confounding. When fitting an 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 because they are generally less variable than the standard weights.

Generalized linear mixed models for binary data: are matching results from penalized quasi-likelihood and numerical integration less biased?

Background: Over time, adaptive Gaussian Hermite quadrature (QUAD) has become the preferred method for estimating generalized linear mixed models with binary outcomes. However, penalized quasi-likelihood (PQL) is still used frequently. In this work, we systematically evaluated whether matching results from PQL and QUAD indicate less bias in estimated regression coefficients and variance parameters via simulation.

Early elevation of serum tumor necrosis factor-α is associated with poor outcome in subarachnoid hemorrhage.

Objective: Subarachnoid hemorrhage (SAH) is associated with inflammation that may mediate poor outcome in SAH. We hypothesize that elevated serum tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6) are associated with vasospasm and poor outcome in SAH.

Methods: In 52 consecutive SAH subjects, we compared TNF-α and IL-6 levels on post-SAH days 0 to 1, 2 to 3, 4 to 5, 6 to 8, and 10 to 14 with respect to vasospasm and to poor outcome at 3 and 6 months.

Refining psychiatric phenotypes for response to treatment: contribution of LPHN3 in ADHD.

Attention deficit/hyperactivity disorder (ADHD) is a heterogeneous disorder characterized by inappropriate levels of attention, hyperactivity, and impulsivity. Although a strong genetic component to the disorder has been established, the molecular genetic underpinnings of this disorder remain elusive. Recently, several studies have reported an association between polymorphisms within the latrophilin 3 gene (LPHN3) and ADHD.

Testing the assumptions for the analysis of survival data arising from a prevalent cohort study with follow-up.

In a prevalent cohort study with follow-up subjects identified as prevalent cases are followed until failure (defined suitably) or censoring. When the dates of the initiating events of these prevalent cases are ascertainable, each observed datum point consists of a backward recurrence time and a possibly censored forward recurrence time. Their sum is well known to be the left truncated lifetime.

Comparative metagenomic study of alterations to the intestinal microbiota and risk of nosocomial Clostridum difficile-associated disease.

This study investigated the relationship between hospital exposures, intestinal microbiota, and subsequent risk of Clostridium difficile-associated disease (CDAD), with use of a nested case-control design. The study included 599 patients, hospitalized from September 2006 through May 2007 in Montreal, Quebec, from whom fecal samples were obtained within 72 h after admission; 25 developed CDAD, and 50 matched controls were selected for analysis. Nonsteroidal anti-inflammatory drugs and antibiotic use were associated with CDAD.