Adjusting for time-varying confounding in the subdistribution analysis of a competing risk

Despite decades of research in the medical literature, assessment of the attributable mortality due to nosocomial infections in the intensive care unit (ICU) remains controversial, with different studies describing effect estimates ranging from being neutral to extremely risk increasing. Interpretation of study results is further hindered by inappropriate adjustment (a) for censoring of the survival time by discharge from the ICU, and (b) for time-dependent confounders on the causal path from infection to mortality. In previous work (Vansteelandt et al. Biostatistics 10:46–59), we have accommodated this through inverse probability of treatment and censoring weighting. Because censoring due to discharge from the ICU is so intimately connected with a patient’s health condition, the ensuing inverse weighting analyses suffer from influential weights and rely heavily on the assumption that one has measured all common risk factors of ICU discharge and mortality. In this paper, we consider ICU discharge as a competing risk in the sense that we aim to infer the risk of ‘ICU mortality’ over time that would be observed if nosocomial infections could be prevented for the entire study population. For this purpose we develop marginal structural subdistribution hazard models with accompanying estimation methods. In contrast to subdistribution hazard models with time-varying covariates, the proposed approach (a) can accommodate high-dimensional confounders, (b) avoids regression adjustment for post-infection measurements and thereby so-called collider-stratification bias, and (c) results in a well-defined model for the cumulative incidence function. The methods are used to quantify the causal effect of nosocomial pneumonia on ICU mortality using data from the National Surveillance Study of Nosocomial Infections in ICU’s (Belgium).     

On the identifiability of copulas in bivariate competing risks models

In competing risks models, the joint distribution of the event times is not identifiable even when the margins are fully known, which has been referred to as the “identifiability crisis in competing risks analysis” (Crowder, 1991). We model the dependence between the event times by an unknown copula and show that identification is actually possible within many frequently used families of copulas. The result is then extended to the case where one margin is unknown. The Canadian Journal of Statistics 41: 291–303; 2013 © 2013 Statistical Society of Canada     

The Impact of Information Sharing on Supply Chain Performance under Asymmetric Information

The use of screening contracts is a common approach to solve supply chain coordination problems under asymmetric information. One main assumption in this context is that managers without specific incentives would rather use their private information strategically than reveal it truthfully. This harms supply chain performance. This study investigates the impact of information sharing in a principal‐agent setting that is typical for many supply chain transactions. We conduct a laboratory experiment to test whether information sharing has an influence on supply chain coordination. We find that information sharing within the supply chain has two positive effects. First, information sharing reduces the inefficiencies resulting from information deficits if there is a certain amount of trust in the supply chain. Second, communication can limit out‐of‐equilibrium behavior with a small impact on the firm's own payoff, but a large impact on the supply chain partner. Furthermore, we find that both effects are amplified when communication takes place in an environment that allows the less informed supply chain party to punish or to reward the better informed party. Although our extended mechanisms substantially enhance the poor performance of the theoretically optimal coordination contract menu, we find no mechanism that implements supply chain performance superior to the theoretically predicted second‐best level.     

Ambivalence Toward Adult Children: Differences Between Mothers and Fathers

The authors examined how ambivalence toward adult children within the same family differs between mothers and fathers and whether patterns of maternal and paternal ambivalence can be explained by the same set of predictors. Using data collected in the Within‐Family Differences Study, they compared older married mothers' and fathers' (N = 129) assessments of ambivalence toward each of their adult children (N = 444). Fathers reported higher levels of ambivalence overall. Both mothers and fathers reported lower ambivalence toward children who were married, better educated, and who they perceived to hold similar values; however, the effects of marital status and education were more pronounced for fathers, whereas the effect of children's value congruence was more pronounced for mothers. Fathers reported lower ambivalence toward daughters than sons, whereas mothers reported less ambivalence toward sons than daughters.     

The challenge of introducing low-carbon industrial practices: Institutional entrepreneurship in the agri-food sector

Contemporary agricultural practices account for a significant share of greenhouse gas emissions. Inspired by the emergent literature on institutional entrepreneurship, we seek to explore mechanisms that affect an actor’s propensity to act in ways that imply suggesting and promoting emission-reducing practice changes. As influences originating outside the organizational field are assumed to constitute such mechanisms, the paper explores their role through a case study of a project run by a public agency. Unlike extant theory, results show that the agency’s propensity to act is not necessarily enhanced by extra-field influences but that such influences also limit the scope for suggesting change that challenges existing industrial practices.