Product-limit survival functions with correlated survival times

A simple variance estimator for product-limit survival functions is demonstrated for survival times with nested errors. Such data arise whenever survival times are observed within clusters of related observations. Greenwood's formula, which assumes independent observations, is not appropriate in this situation. A robust variance estimator is developed using Taylor series linearized values and the between-cluster variance estimator commonly used in multi-stage sample surveys. A simulation study shows that the between-cluster variance estimator is approximately unbiased and yields confidence intervals that maintain the nominal level for several patterns of correlated survival times. The simulation study also shows that Greenwood's formula underestimates the variance when the survival times are positively correlated within a cluster and yields confidence intervals that are too narrow. Extension to life table methods is also discussed.     

Rich Ties and Innovative Knowledge Transfer within a Firm

We show that contacts in formal, informal and especially multiplex networks explain transfer of innovative knowledge in an organization. The contribution of informal contacts has been much acknowledged, while that of formal contacts did not receive much attention in the literature in recent decades. No study thus far has included both these different kinds of contacts in a firm, let alone considered their combined effect. The exact overlap between formal as well as informal contacts between individuals, forming multiplex or what we call rich ties because of their contribution, especially drives the transfer of new, innovative knowledge in a firm. Studying two cases in very different settings suggests these rich ties have a particularly strong effect on knowledge transfer in an organization, even when controlling for the strength of ties. Some of the effects on knowledge transfer in an organization previously ascribed to either the formal network or the informal network may actually be due to their combined effect in a rich tie.     

Addressing elder abuse: the Waterloo restorative justice approach to elder abuse project

The Community Care Access Centre (CCAC) of Waterloo Region, in partnership with a number of other social service agencies, designed and implemented a restorative justice model applicable to older adults who have been abused by an individual in a position of trust. The project was very successful in building partnerships, as many community agencies came together to deal with the problem of elder abuse. The program also raised the profile of elder abuse in the community. However, despite intensive efforts, referrals to the restorative justice program were quite low. Because of this, the program moved to a new organizational model, the Elder Abuse Response Team (EART), which has retained the guiding philosophy of restorative justice but has broadened the mandate. The team has evolved into a conflict management system that has multiple points of entry for cases and multiple options for dealing with elder abuse. The team has developed a broad range of community partners who can facilitate referrals to the EART and also can help to provide an individualized response to each case. The transition to the EART has been successful, and the number of referrals has increased significantly.     

Investigation of age–treatment interaction in the SPACE trial using different statistical approaches

Selection of treatments to fit the specific needs for a certain patient is one major challenge in modern medicine. Personalized treatments rely on established patient–treatment interactions. In recent years, various statistical methods for the identification and estimation of interactions between relevant covariates and treatment were proposed. In this article, different available methods for detection and estimation of a covariate–treatment interaction for a time-to-event outcome, namely the standard Cox regression model assuming a linear interaction, the fractional polynomials approach for interaction, the modified outcome approach, the local partial-likelihood approach, and STEPP (Subpopulation Treatment Effect Pattern Plots) were applied to data from the SPACE trial, a randomized clinical trial comparing stent-protected angioplasty (CAS) to carotid endarterectomy (CEA) in patients with symptomatic stenosis, with the aim to analyse the interaction between age and treatment. Time from primary intervention to the first relevant event (any stroke or death) was considered as outcome parameter. The analyses suggest a qualitative interaction between patient age and treatment indicating a lower risk after treatment with CAS compared to CEA for younger patients, while for elderly patients a lower risk after CEA was observed. Differences in the statistical methods regarding the observed results, applicability, and interpretation are discussed.     

School environment and risk preferences: Experimental evidence

Using a field experiment with high school students, we evaluate the development of risk preferences. Examining the impact of school characteristics on preference development reveals both peer and quality effects. For the peer effect, individuals in schools with a higher percentage of students on free or reduced lunches (hence a higher proportion of low-income peers with whom to interact) are significantly more risk averse. For the quality effect, individuals in schools with smaller class sizes and a higher percentage of educators with advanced degrees have higher, more moderate levels of risk aversion. We further discuss economic, cognitive and emotional development theories of risk preferences. Data show demographic-related patterns: girls are more risk averse on average, while taller and nonwhite individuals are more risk tolerant.