A Method to Compare Two Samples of Recurrence Data

This paper presents a nonparametric comparison of two samples of units subject to recurrent events. The method is illustrated with applications to the repair of locomotive braking grids and to recurrent bladder tumors in patients. This revised version was published online in July 2006 with corrections to the Cover Date.     

Environmental scanning—Does it help the chief executive?

Firms must correctly identify and analyze the nature of their strategic environments, their strategic oppurtunities and problems, and, formulate the precise strategy sets for corporate strategy for accomplishing the chosen organizational objectives and goals. This articles reports on a survey. Chief executives of industrial corporations provided their insights and experience (see Appendix I) and the findings are analyzed for the implications for other practising chief executives. The nature of environment which is strategic to a particular firm has considerable influence upon the firm's choice of strategies. The correct understanding of this influence is critical to the firm's organizational effectiveness. Only after a correct understanding can the chief executive formulate the precise mix of strategies and meld them in the strategy sets of the corporate strategy.The major findings indicate that the levels of difficulty experienced in accomplishing firm's objectives and goals depend upon the perceived nature of complexity, unpredictability and dynamism of the firm's strategic environments. The levels of clarity on strategic issues also depend upon these same attributes of environments. The formulation of strategy sets of corporate strategy are indicative of the ways by which the chief executive and his management team expect the firm to achieve its major objectives and goals by monitoring the strategy sets to keep in tune with the changing realities of the firm's strategic environments. General management, marketing and finance, were the vital group strategies, followed by production and research and development. External relations, personnel and procurement were the least important strategies. Firms operating in simple and stable environments experienced the least difficulty in achieving corporate goals, while firms in dynamic and complex environments experienced the greatest difficulty.     

The mixed model for survey regression estimation

Estimation of the population mean under the regression model with random components is considered. Conditions under which the random components regression estimator is design consistent are given. It is shown that consistency holds when incorrect values are used for the variance components. The regression estimator constructed with model parameters that differ considerably from the true parameters performed well in a Monte Carlo study. Variance estimators for the regression predictor are suggested. A variance estimator appropriate for estimators constructed with a biased estimator for the between-group variance component performed well in the Monte Carlo study.     

Evaluating the ROC performance of markers for future events

Receiver operating characteristic (ROC) curves play a central role in the evaluation of biomarkers and tests for disease diagnosis. Predictors for event time outcomes can also be evaluated with ROC curves, but the time lag between marker measurement and event time must be acknowledged. We discuss different definitions of time-dependent ROC curves in the context of real applications. Several approaches have been proposed for estimation. We contrast retrospective versus prospective methods in regards to assumptions and flexibility, including their capacities to incorporate censored data, competing risks and different sampling schemes. Applications to two datasets are presented.     

The issue of consent in research that administers drugs of addiction to addicted persons

In addiction, impaired control over drug use raises questions about the capacity of addicted persons to consent to participate in research studies in which they are given their drug of addiction. We review the case for doing such research, and the arguments that addiction does, and does not, prevent addicted persons from consenting to such research. We argue for a more nuanced view that acknowledges that while in some situations addiction impairs decision-making capacity, it does not eliminate such capacity. We conclude with some suggestions for recruiting addicted subjects and designing experiments in ways to obtain free and informed consent.     

Task Interdependence as a Moderator of the Relation Between Group Control and Performance

Data were collected from the managers of 77groups in a large service organization and a largemanufacturing organization. The results revealed thatthe relation between group control over decision making and group performance became more positive withincreased levels of task interdependence. The mainimplication of the findings is that increasing groupcontrol over decisions may result in high performance only for groups that are highly taskinterdependent. The performance of groups that are lowin task interdependence may suffer when provided withgroup-level control of decisions.     

Ecosystem processes along an urban-to-rural gradient

In order to understand the effect of urban development on the functioning of forest ecosystems, during the past decade we have been studying red oak stands located on similar soil along an urban-rural gradient running from New York City ro rural Litchfield County, Connecticut. This paper summarizes the results of this work. Field measurements, controlled laboratory experiments, and reciprocal transplants documented soil pollution, soil hydrophobicity, litter decomposition rates, total soil carbon, potential nitrogen mineralization, nitrification, fungal biomass, and earthworm populations in forests along the 140 × 20 km study transect. The results revealed a complex urban-rural environmental gradient. The urban forests exhibit unique ecosystem structure and function in relation to the suburban and rural forest stands these are likely linked to stresses of the urban environment such as air pollution, which has also resulted in elevated levels of heavy metals in the soil, the positive effects of the heat island phenomenon, and the presence of earthworms. The data suggest a working model to guide mechanistic work on the ecology of forests along urban-to-rural gradients, and for comparison of different metropolitan areas.