Increasing the sample size at interim for a two‐sample experiment without Type I error inflation

For the case of a one‐sample experiment with known variance σ²=1, it has been shown that at interim analysis the sample size (SS) may be increased by any arbitrary amount provided: (1) The conditional power (CP) at interim is ?50% and (2) there can be no decision to decrease the SS (stop the trial early). In this paper we verify this result for the case of a two‐sample experiment with proportional SS in the treatment groups and an arbitrary common variance. Numerous authors have presented the formula for the CP at interim for a two‐sample test with equal SS in the treatment groups and an arbitrary common variance, for both the one‐ and two‐sided hypothesis tests. In this paper we derive the corresponding formula for the case of unequal, but proportional SS in the treatment groups for both one‐sided superiority and two‐sided hypothesis tests. Finally, we present an SAS macro for doing this calculation and provide a worked out hypothetical example. In discussion we note that this type of trial design trades the ability to stop early (for lack of efficacy) for the elimination of the Type I error penalty. The loss of early stopping requires that such a design employs a data monitoring committee, blinding of the sponsor to the interim calculations, and pre‐planning of how much and under what conditions to increase the SS and that this all be formally written into an interim analysis plan before the start of the study. Copyright © 2009 John Wiley & Sons, Ltd.     

Occupational safety and profit maximization: Friends or foes?

The rise of the Industrial Revolution is often depicted as a cause of hazardous working conditions and is skillfully epitomized in William Blake's tale of a child chimney sweeper. Conventional wisdom puts firm profit in conflict with occupational safety. We reexamine this argument noting that injuries are very costly to firms because they lead to higher wage premiums, worker compensation, and costly work stoppages. We hypothesize that it is precisely for these reasons that firms in the industries with dangerous working conditions have the strongest incentives to innovate and substitute more capital for labor. Using a longitudinal panel of U.S. industries, we test and confirm our hypothesis that higher injury rates lead to higher capital stock per worker, over time. Moreover, our estimates suggest that firms provide more capital and equipment per worker than what would have been there based solely on the compensating wage differential.     

Charting a Discursive Field: Environmentalists for U.S. Population Stabilization*

This article seeks to extend our understanding of the forces that shape social movement messages. Using a framework that focuses on a movement's discursive field, I analyze the U.S. movement for population stabilization, which is made up of groups that call for stricter limits on immigration to the United States as a means to forestall environmental decline. Drawing upon data from a range of sources, including the Web sites of 10 environment‐oriented immigration‐reduction organizations, I make the case that this movement's particular field is composed of the discursive repertoires (or messages) of a set of environmental and nonenvironmental social actors and three central discourses: science, political economy, and nationalism. I argue that the movement's relative lack of success is partially attributable to its position in the discursive field in which it must operate.     

The Influence of Volunteer Recruitment Practices and Expectations on the Development of Volunteers’ Psychological Contracts

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - Volunteer recruitment and retention continue to be important issues for not-for-profit organisations. A theoretical...     

The Globalization of Penal Space in Nineteenth-Century Malta

In the second half of the nineteenth century an unprecedented number of prisons were built across the Western-influenced world. However, many more developed from repurposed and modified buildings. By applying space syntax analysis to examples from the then British colony of Malta, this article investigates the commonalities of penal space across a series of purpose-built and refashioned prisons, taking into consideration key architectural phases resulting from remodelling. Rejecting the notion that Maltese developments are merely symptomatic of British colonialism, the spread of Western prisons is cast in terms of wider trends and the global spread of a particular type of penal space.     

Role ambiguity and volunteer board member performance in nonprofit sport organizations

We explore the relationship between multidimensional role ambiguity and individual board member performance within nonprofit voluntary sport organizations. Role ambiguity accounted for 29 percent of the variance in perceived board member performance, and ambiguity about one's responsibilities was the strongest predictor. These findings extend our understanding of the drivers of individual board member performance within voluntary sport organizations and the multidimensional nature of role ambiguity. The study supports previous arguments that knowing what to do is fundamental to one's performance, and more critical than knowing how to do it, and what difference it makes.     

Intergenerational Mobility in Relative Educational Attainment and Health-Related Behaviours

Social Indicators Research - Research on intergenerational social mobility and health-related behaviours yields mixed findings. Depending on the direction of mobility and the type of mechanisms...