On Existence of Maximum Likelihood Estimators in Exponential Families

We propose a simple necessary and sufficient condition for existence of maximum likelihood estimators in a large class of canonical exponential families. We give an application to log-spline families.     

A branching method for the fixed charge transportation problem

This paper presents a branching method for the solution of the fixed charge transportation problem. Starting with a linear formulation of the problem, we develop the method which converges to the optimal solution. The method is based on the computation of a lower bound and an upper bound embedded within a branching process. We present a detailed numerical example to illustrate the proposed method.     

Modifying a central composite design to model the process mean and variance when there are hard-to-change factors

Summary.  An important question within industrial statistics is how to find operating conditions that achieve some goal for the mean of a characteristic of interest while simultaneously minimizing the characteristic's process variance. Often, people refer to this kind of situation as the robust parameter design problem. The robust parameter design literature is rich with ways to create separate models for the mean and variance from this type of experiment. Many times time and/or cost constraints force certain factors of interest to be much more difficult to change than others. An appropriate approach to such an experiment restricts the randomization, which leads to a split-plot structure. The paper modifies the central composite design to allow the estimation of separate models for the characteristic's mean and variances under a split-plot structure. The paper goes on to discuss an appropriate analysis of the experimental results. It illustrates the methodology with an industrial experiment involving a chemical vapour deposition process for the manufacture of silicon wafers. The methodology was used to achieve a silicon layer thickness value of 485 Å while minimizing the process variation.     

A new model and class of designs for mixture experiments with process variables

Experiments that involve the blending of several components are known as mixture experiments. In some mixture experiments, the response depends not only on the proportion of the mixture components, but also on the processing conditions, A new combined model is proposed which is based on Taylor series approximation and is intended to be a compromise between standard mixture models and standard response surface models. Cost and/or time constraints often limit the size of industrial experiments. With this in mind, we present a new class of designs that will accommodate the fitting of the new combined model.     

A test for the global minimum variance portfolio for small sample and singular covariance

AStA Advances in Statistical Analysis - Recently, a test dealing with the linear hypothesis for the global minimum variance portfolio weights was obtained under the assumption of non-singular...     

Sociologist Austin Turk and Policing: Structural Reinforcers and Reversals of the Positional Authority of Police

Austin Turk (1969) offers a distinctly sociological explanation of policing by theorizing that structural reinforcers (e.g., older police officer, younger citizen) and reversals (e.g., younger police officer, older citizen) of the situationally absolute positional authority of police officers affect the relationship between police officers and citizens. To this point, however, there have been only three direct tests of Turk’s theory ( Greenleaf and Lanza‐Kaduce, 1995 ; Lanza‐Kaduce and Greenleaf, 2000 ; Weidner and Terrill, 2005 ). All have examined overt conflict and the results are mixed. The present research therefore adds a fourth test of Turk’s (1969) theory to the sociological literature by examining the effects of structural reinforcers and reversals on citizens’ perceptions of the legitimacy and propriety of police actions during routine traffic stop encounters. Net of control measures, including the legal reason for the traffic stop, and extra‐legal measures, such as driver gender, the data provide modest to strong support for parts of Turk’s (1969) theory and absolutely no support for others. The conclusion of the present study is that more research is needed to determine whether Turk (1969) is correct in theorizing that there is a sociology, and not just a social psychology, to police‐citizen encounters.