Bayesian MARS

A Bayesian approach to multivariate adaptive regression spline (MARS) fitting (Friedman, 1991) is proposed. This takes the form of a probability distribution over the space of possible MARS models which is explored using reversible jump Markov chain Monte Carlo methods (Green, 1995). The generated sample of MARS models produced is shown to have good predictive power when averaged and allows easy interpretation of the relative importance of predictors to the overall fit.     

Limited information likelihood analysis of survey data

Analysts of survey data are often interested in modelling the population process, or superpopulation, that gave rise to a 'target' set of survey variables. An important tool for this is maximum likelihood estimation. A survey is said to provide limited information for such inference if data used in the design of the survey are unavailable to the analyst. In this circumstance, sample inclusion probabilities, which are typically available, provide information which needs to be incorporated into the analysis. We consider the case where these inclusion probabilities can be modelled in terms of a linear combination of the design and target variables, and only sample values of these are available. Strict maximum likelihood estimation of the underlying superpopulation means of these variables appears to be analytically impossible in this case, but an analysis based on approximations to the inclusion probabilities leads to a simple estimator which is a close approximation to the maximum likelihood estimator. In a simulation study, this estimator outperformed several other estimators that are based on approaches suggested in the sampling literature.     

Discrete distributions with maximum expected value of the maximum

We give an upper bound for the expected value of the largest order statistic of a simple random sample of size n from a discrete distribution on N points. We also characterize the distributions that attain such bound. In the particular case n=2, we obtain a characterization of the discrete uniform distribution. © 1998 Elsevier Science B.V. All rights reserved.     

A new class of measurement-error models,with applications to dietary data

Measurement-error modelling occurs when one cannot observe a covariate, but instead has possibly replicated surrogate versions of this covariate measured with error. The vast majority of the literature in measurement-error modelling assumes (typically with good reason) that given the value of the true but unobserved (latent) covariate, the replicated surrogates are unbiased for latent covariate and conditionally independent. In the area of nutritional epidemiology, there is some evidence from biomarker studies that this simple conditional independence model may break down due to two causes: (a) systematic biases depending on a person's body mass index, and (b) an additional random component of bias, so that the error structure is the same as a one-way random-effects model. We investigate this problem in the context of (1) estimating distribution of usual nutrient intake, (2) estimating the correlation between a nutrient instrument and usual nutrient intake, and (3) estimating the true relative risk from an estimated relative risk using the error-prone covariate. While systematic bias due to body mass index appears to have little effect, the additional random effect in the variance structure is shown to have a potentially important effect on overall results, both on corrections for relative risk estimates and in estimating the distribution of usual nutrient intake. However, the effect of dietary measurement error on both factors is shown via examples to depend strongly on the data set being used. Indeed, one of our data sets suggests that dietary measurement error may be masking a strong risk of fat on breast cancer, while for a second data set this masking is not so clear. Until further understanding of dietary measurement is available, measurement-error corrections must be done on a study-specific basis, sensitivity analyses should be conducted, and even then results of nutritional epidemiology studies relating diet to disease risk should be interpreted cautiously.     

New Organizational Forms for Competing in Highly Dynamic Environments: the Network Paradigm

Turbulence and rapid change in the business environment have been associated for some time with the development of new network organizational forms which put various types of strategic alliance and other inter-organizational collaborations into effect. This paper traces the rationale for the formation of such networks and the associated vertical disaggregation of functions and implications for internal organizational design. This leads to the proposal of a classification framework for network forms. Using the dimensions of volatility of environmental change on the one hand, and the type of inter-organizational relationship involved (collaborative or transactional) on the other hand, network forms are classified as: hollow networks, flexible networks, value-added networks and virtual networks. In each case it is possible to identify the environmental and organizational contingencies most likely to be associated with the emergence and adoption of a particular type of network arrangement. This argument leads to the identification of a new research agenda which has the goals of developing more robust conceptualizations of network characteristics; better understanding the contingencies surrounding the emergence of network forms and their relative efficiencies and specifying some of the major implications of network formation for internal organizational design. In parallel the paper identifies a number of managerial implications for setting strategic priorities and developing appropriate management systems in these new organizational contexts.     

Competitive Advantage, Quality Strategy and the Role of Marketing

The improvement of product and service quality has been widely discussed in the literature as an appropriate competitive strategy for achieving sustainable competitive advantage. However, neither the linkage between competitive strategy and quality, nor the role of marketing in the implementation of quality-based competitive strategy, has received detailed attention in the marketing and strategy literatures. This paper explores the interface between marketing and quality management in seller organizations, by developing a contingency model of quality strategy. This model is grounded in the literatures of marketing, strategy and quality management, and the perceptions of managers uncovered in exploratory interviews.     

IRS offers safe harbor in physician employment contracts

Last year, the Internal Revenue Service (IRS) issued Revenue Procedure 93-19 (Rev. Proc. 93-19), which provides guidelines regarding service and other contracts involving facilities financed with tax-exempt bonds. Rev. Proc. 93-19 creates four "safe harbors" for certain contracts signed by tax-exempt organizations that will not jeopardize the organizations' tax-exempt bond interest. Those guidelines and methods for complying with them are the subject of the following article. "Health Law" is a regular feature of Physician Executive contributed by Epstein Becker & Green. Mark Lutes of the law firm's Washington, D.C., offices serves as editor of the column.     

Delivery and funding are provincial matters in Canada

The following article is one of a series that deal with the provision of health care services around the world. Other countries in the series include Germany, Italy, Japan, Mexico, the Netherlands, and the United States. Countries scheduled for coverage in the series include Austria, France, Singapore, Spain, and the United Kingdom. The countries are described using a grid of characteristics so that comparisons may be made more easily. All of the analyses, along with further comparative data, will be gathered into a freestanding book to be published later in the year. Dr. Mendoza serves as editor for the project.