An Algorithm for the Maximum Likelihood Problem on Evolutionary Trees

We investigate the problem of reconstructing evolutionary trees with maximum likelihood (MLET). In the MLET problem, a set of genetic sequences is given and a feasible solution is sought, consisting of an evolutionary tree (where general nodes correspond to sequences and input sequences occur as leaves) along with assignments for the interior nodes. Due to the difficulty of solving the MLET directly, we consider two restricted versions of the problem: the ancestral maximum likelihood (AML) and the maximum parsimony (MP) problems. If we let d_e denote the number of different characters occurring in two nodes linked by edge e, then the objective function of the AML problem is min ∑_{eσ E(T)} H(d_e/k), where H is the entropy function and k is the length of each sequence. In the MP we consider the objective function min σ_{e∊ E(T)} d_e/k. Both the AML and the MP are NP-hard. We propose a new approach for computing solutions for these problems, based on genetic algorithms.     

Genetics of pathological gambling

Pathological gambling (PG) is an impulse control disorder and a model behavioral addiction. Familial factors have been observed in clinical studies of pathological gamblers, and twin studies have demonstrated a genetic influence contributing to the development of PG. Serotonergic, noradrenergic, and dopaminergic dysfunction have been reported as biological factors contributing to the pathophysiology of PG. Molecular genetic techniques have been used to investigate the role of genetic factors in PG. Molecular genetic research has identified specific allele variants of candidate genes corresponding to these neurotransmitter systems to be associated with PG. Associations have been reported between pathological gamblers and allele variants of polymorphisms at dopamine receptor genes, the serotonin transporter gene, and the monoamine-oxidase A gene. Although preliminary data suggest that some of these differences are gender-specific, more research needs to be performed to substantiate gender-specific genetic contributions to the development of pathological gambling. The review of the current findings on genetics of PG suggests that liability to PG is in part mediated by genetic factors. Additional studies are needed to replicate and extend these findings, as well as to better understand the influence of specific allelic variants to differences in biological and behavioral functioning.     

Some issues related to the topological aggregation of preferences: addendum

 The purpose of this addendum is to correct some results published in our paper “Some issues related to the topological aggregation of preferences” (SCW (1992) 9: 213–227). Received: 28 November 1992/Accepted: 22 April 1996     

Process of Symptom Production and Patterns of Symptom Maintenance

In the search for the process of symptom production, on the one hand, and for the patterns of symptom maintenance, on the other, lies the key difference between the two main orientations in the field of family therapy; the psychodynamic and the system-oriented approaches. They imply conceptual and operational hypotheses stemming from different logics, different sets of data, different lines of inquiry and, alas, different treatment strategies. Clearly distinctive traits of each of these two lines are discussed and exemplified, with special emphasis on the interactional, systemic view.     

A Test For Heteroscedasticity in a Limited Dependent Variable Model

Limited Dependent Variable models arise, for example, when the dependent variable is necessarily non-negative. When these models are estimated under the incorrect assumption of homoscedasticity, serious consequences have been found. It is therefore important to test for its existence. In this paper, we make use of the Lagrange multiplier procedure to derive a test for heteroscedasticity in the Tobit model.     

Managing internationally: International dimensions of the managerial task

Following a review of the literature on managing internationally, Juan Roure, José Luis Alvarez, Carlos Garcia-Pont and José Nueno challenge the conventional view. This says that international managers are generalists with a global mind set, and that in the process of internationalisation the internal and external tasks of the manager are affected equally.The authors use field research to demonstrate that global managers are less in evidence than is commonly believed, regional management is more widespread than global management, and the internationalisation of managers affects their internal activities more than their external ones. Internal and external tasks of managers are mapped, and future lines for research identified.     

On identifiability of parametric statistical models

Summary This is a review article on statistical identifiability. Besides the definition of the main concepts, we deal with several questions relevant to the statistician: parallelism between parametric identifiability and sample sufficiency; relationship of identifiability with measures of sample information and with the inferential concept of estimability; several strategies of making inferences in unidentifiable models with emphasis on the distinct behaviour of the classical and Bayesian approaches. The concepts, ideas and methods discussed are illustrated with simple examples of statistical models. Centro de Análise e Processamento de Sinais da UTL     

Joint regression modeling for missing categorical covariates in generalized linear models

Missing covariates data is a common issue in generalized linear models (GLMs). A model-based procedure arising from properly specifying joint models for both the partially observed covariates and the corresponding missing indicator variables represents a sound and flexible methodology, which lends itself to maximum likelihood estimation as the likelihood function is available in computable form. In this paper, a novel model-based methodology is proposed for the regression analysis of GLMs when the partially observed covariates are categorical. Pair-copula constructions are used as graphical tools in order to facilitate the specification of the high-dimensional probability distributions of the underlying missingness components. The model parameters are estimated by maximizing the weighted log-likelihood function by using an EM algorithm. In order to compare the performance of the proposed methodology with other well-established approaches, which include complete-cases and multiple imputation, several simulation experiments of Binomial, Poisson and Normal regressions are carried out under both missing at random and non-missing at random mechanisms scenarios. The methods are illustrated by modeling data from a stage III melanoma clinical trial. The results show that the methodology is rather robust and flexible, representing a competitive alternative to traditional techniques.     

Strategic management in a firm of consulting engineers

This article describes the introduction of strategic management in a large and diversified company of consulting engineers in Brazil. This was done by a massive strategic planning effort in which the 60 top people of the company actively participated. This approach was chosen to produce both a comprehensive corporate strategy and strategic management capability throughout the company. The project therefore gave as much attention to training and guidance as to planning itself. Psychological, organizational and ‘political’ factors were taken seriously into account. Project management was a good joint-venture between some top people inside and some external consultants, strongly interacting with each other. The project resulted not only in plans, but also in decisions, including tidying-up the divisional structure of the firm. The article evaluates the project to determine success factors in such undertakings. It is interesting for managers to appreciate the factors involved in efforts to produce plans, develop managers and reorient a company at the same time. It is also interesting because it shows a fruitful, although demanding role for management consultants in strategic reorientations: more committed, more ‘on-line’ than experts submitting recommendations; less amorphous and more performance-oriented than organizational development gurus.