Valuing water resources in developing countries: A semiparametric approach to valuation models

Valuation of projects for the preservation of water resources provides important information to policy makers and funding institutions. Standard contingent valuation models rely on distributional assumptions to provide welfare measures. Deviations from assumed and actual distribution of benefits are important when designing policies in developing countries, where inequality is a concern. This article applies semiparametric methods to obtain estimates of the benefit from a project for the preservation of an important Brazilian river basin. These estimates lead to significant differences from those obtained using the standard parametric approach.

Bridging the gap between different statistical approaches: An integrated framework for modelling

This paper proposes a template for modelling complex datasets that integrates traditional statistical modelling approaches with more recent advances in statistics and modelling through an exploratory framework. Our approach builds on the well-known and long standing traditional idea of 'good practice in statistics' by establishing a comprehensive framework for modelling that focuses on exploration, prediction, interpretation and reliability assessment, a relatively new idea that allows individual assessment of predictions. The integrated framework we present comprises two stages. The first involves the use of exploratory methods to help visually understand the data and identify a parsimonious set of explanatory variables. The second encompasses a two step modelling process, where the use of non-parametric methods such as decision trees and generalized additive models are promoted to identify important variables and their modelling relationship with the response before a final predictive model is considered. We focus on fitting the predictive model using parametric, non-parametric and Bayesian approaches. This paper is motivated by a medical problem where interest focuses on developing a risk stratification system for morbidity of 1,710 cardiac patients given a suite of demographic, clinical and preoperative variables. Although the methods we use are applied specifically to this case study, these methods can be applied across any field, irrespective of the type of response.

Predicting Xerostomia induced by IMRT treatments: A logistic regression approach

Radiotherapy is one of the main treatments used against cancer. Radiotherapy uses radiation to destroy cancerous cells trying, at the same time, to minimize the damages in healthy tissues. The planning of a radiotherapy treatment is patient dependent, resulting in a lengthy trial and error procedure until a treatment complying as most as possible with the medical prescription is found. Intensity Modulated Radiation Therapy (IMRT) is one technique of radiation treatment that allows the achievement of a high degree of conformity between the area to be treated and the dose absorbed by healthy tissues. Nevertheless, it is still not possible to eliminate completely the potential treatments’ side-effects. In this retrospective study we use the clinical data from patients with head-and-neck cancer treated at the Portuguese Institute of Oncology of Coimbra and explore the possibility of classifying new and untreated patients according to the probability of xerostomia 12 months after the beginning of IMRT treatments by using a logistic regression approach. The results obtained show that the classifier presents a high discriminative ability in predicting the binary response “at risk for xerostomia at 12 months”

Bayesian genetic parameters for body weight and survival of Nile tilapia farmed in Brazil

The objective of this study was to estimate genetic parameters for survival and weight of Nile tilapia (Oreochromis niloticus), farmed in cages and ponds in Brazil, and to predict genetic gain under different scenarios. Survival was recorded as a binary response (dead or alive), during harvest time in the 2008 grow-out period. Genetic parameters were estimated using a Bayesian mixed linear-threshold animal model via Gibbs sampling. The breeding population consisted of 2,912 individual fish, which were analyzed together with the pedigree of 5,394 fish. The heritabilities estimates, with 95% posterior credible intervals, for tagging weight, harvest weight and survival were 0.17 (0.09-0.27), 0.21 (0.12-0.32) and 0.32 (0.22-0.44), respectively. Credible intervals show a 95% probability that the true genetic correlations were in a favourable direction. The selection for weight has a positive impact on survival. Estimated genetic gain was high when selecting for harvest weight (5.07%), and indirect gain for tagging weight (2.17%) and survival (2.03%) were also considerable.

L’assistance médicalisée pour mourir demandée dans le cadre des soins de fin de vie : enjeux d’une éthique réflexive et critique pour l’humanisation de la mort

Par une approche analytique, cette étude en éthique clinique a examiné la problématique de la demande d’assistance médicalisée pour mourir formulée dans le cadre des soins de fin de vie. Partant du fait que cette demande sollicite les soignants dans leur savoir et leur savoir-faire, surtout dans leur savoir-être, cette étude rend d’abord compte d’un fait : bon gré mal gré l’interdit de l’euthanasie par la loi et la déontologie médicale, ainsi que le débat contradictoire à son sujet qui dure déjà voici quelques décennies, il arrive de temps à autres que les soignants œuvrant en soins de fin de vie, soient confrontés à une demande d’assistance médicalisée pour mourir. Cette demande qui émane de certaines personnes en fin de vie et / ou de leurs proches, est souvent source de malaise pour les soignants à l’endroit de qui elle crée des défis majeurs et fait naître des dilemmes éthiques importants. Plus particulièrement, cette demande interroge toujours la finalité même des soins de fin de vie : est-ce que l’aide pour mourir fait partie de ces soins ? En réponse à cette question difficile, cette démarche réflexive de soignant chercheur en éthique montre qu’il est difficile de donner une réponse binaire en forme de oui / non ; il est difficile de donner une réponse d’application universalisable, et de définir une généralisable conduite à tenir devant une telle demande, car chaque cas est singulier et unique à son genre. Cette étude montre prioritairement que l’humanisation de la mort est à la fois un enjeu éthique important et un défi majeur pour notre société où la vie des individus est médicalisée de la naissance à la mort. En conséquence, parce que la demande d’assistance médicalisée pour mourir sollicite les soignants dans leur savoir et leur savoir-faire, cette étude montre toute l’importance de la réflexivité et de la créativité que doivent développer les soignants pour apporter une réponse constructive à chaque demande : une réponse humanisant le mourir et la mort elle-même, c’est-à-dire une réponse qui soit, sur le plan éthique, raisonnable et cohérente, une réponse qui soit sur le plan humain, porteuse de sens. D’où, outre l’axiologie, cette démarche réflexive montre que l’interdisciplinarité, la sémantique, l’herméneutique et les grilles d’analyse en éthique, constituent des outils réflexifs efficaces pouvant mieux aider les soignants dans leur démarche. Sur quelles bases éthiques, les soignants doivent-ils examiner une demande d’assistance médicalisée pour mourir, demande qui se présente toujours sous la forme d’un dilemme éthique? Cette question renvoie entre autre au fait que cette demande sollicite profondément les soignants dans leur savoir-être en relation des soins de fin de vie. Aussi bonnes les unes que les autres, qu’on soit pour ou contre l’euthanasie, plusieurs stratégies et méthodes d’analyse sont proposées aux soignants pour la résolution des conflits des valeurs et des dilemmes éthiques. Mais, ce n’est pas sur cette voie-là que cette étude invite les soignants. C’est plutôt par leur réflexivité et leur créativité, enrichies principalement par leur humanisme, leur expérience de vie, leur intuition, et secondairement par les différentes méthodes d’analyse, que selon chaque contexte, les soignants par le souci permanent de bien faire qui les caractérisent, trouveront toujours par eux-mêmes ce qui convient de faire dans l’ici et maintenant de chaque demande. C’est pourquoi, devant une demande d’assistance médicalisée pour mourir qui leur est adressée dans le cadre des soins de fin de vie, cette démarche éthique invite donc les soignants à être « des cliniciens créatifs, des praticiens réflexifs» . C’est pour cette raison, sur le plan proprement dit de la réflexion éthique, cette étude fait apparaître les repères de l’éthique humaniste de fin de vie comme bases axiologiques sur lesquels les soignants peuvent construire une démarche crédible pour répondre au mieux à cette demande. L’éthique humaniste de fin de vie située dans le sillage de l’humanisme médical , où l’humain précède le médical, renvoie au fait qu’en soins de fin de vie où émerge une demande d’aide à la mort, entre le demandeur de cette aide et le soignant, tout doit être basé sur une confiante relation d’homme à homme, même si du côté du soignant, son savoir être dans cette relation est aussi enrichi par sa compétence, ses connaissances et son expérience ou son savoir-faire. Basée sur l’humanité du soignant dans la démarche de soins, l’éthique humaniste de fin de vie en tant que pratique réflexive émerge de la créativité éthique du soignant lui-même et de l’équipe autour de lui ; et cette éthique se situe entre interrogation et transgression, et se définit comme une éthique « du vide-de-sens-à-remplir » dans un profond souci humain de bien faire. Car, exclue l’indifférence à la demande de l’assistance médicalisée pour mourir, son acceptation ou son refus par le soignant, doit porter sur l’humanisation de la mort. Cette dernière étant fondamentalement définie par rapport à ce qui déshumanise la fin de vie.

A simple test of momentum in foreign exchange markets

This study proposes a new method for testing for the presence of momentum in nominal exchange rates, using a probabilistic approach. We illustrate our methodology estimating a binary response model using information on local currency / US dollar exchange rates of eight emerging economies. After controlling for important variables a§ecting the behavior of exchange rates in the short-run, we show evidence of exchange rate inertia; in other words, we Önd that exchange rate momentum is a common feature in this group of emerging economies, and thus foreign exchange traders participating in these markets are able to make excess returns by following technical analysis strategies. We Önd that the presence of momentum is asymmetric, being stronger in moments of currency depreciation than of appreciation. This behavior may be associated with central bank intervention

Choosing the number of doses and the cohort size for phase I dose-escalation studies

This paper reviews Bayesian procedures for phase 1 dose-escalation studies and compares different dose schedules and cohort sizes. The methodology described is motivated by the situation of phase 1 dose-escalation studiesin oncology, that is, a single dose administered to each patient, with a single binary response ("toxicity"' or "no toxicity") observed. It is likely that a wider range of applications of the methodology is possible. In this paper, results from 10000-fold simulation runs conducted using the software package Bayesian ADEPT are presented. Four designs were compared under six scenarios. The simulation results indicate that there are slight advantages of having more dose levels and smaller cohort sizes.

Feasible estimation of generalized linear mixed models (GLMM) with weak dependency between groups

This paper presents a two-step pseudo likelihood estimation technique for generalized linear mixed models with the random effects being correlated between groups. The core idea is to deal with the intractable integrals in the likelihood function by multivariate Taylor's approximation. The accuracy of the estimation technique is assessed in a Monte-Carlo study. An application of it with a binary response variable is presented using a real data set on credit defaults from two Swedish banks. Thanks to the use of two-step estimation technique, the proposed algorithm outperforms conventional pseudo likelihood algorithms in terms of computational time.

Aspectos do mercado eleitoral brasileiro: análise econométrica do impacto dos gastos de campanha nas eleições para a Câmara e o Senado de 2002

Esta dissertação de mestrado em economia foi motivada por uma questão complexa bastante estudada na literatura de economia política nos dias de hoje: as formas como campanhas políticas afetam votação em uma eleição. estudo procura modelar mercado eleitoral brasileiro para deputados federais senadores. Através de um modelo linear, conclui-se que os gastos em campanha eleitoral são fatores decisivos para eleição de um candidato deputado federal. Após reconhecer que variável que mede os gastos em campanha possui erro de medida (devido ao famoso "caixa dois", por exemplo), além de ser endógena uma vez que candidatos com maiores possibilidades de conseguir votos conseguem mais fontes de financiamento -, modelo foi estimado por variáveis instrumentais. Para senadores, utilizando modelos lineares modelos com variável resposta binaria, verifica-se também importância, ainda que em menor escala, da campanha eleitoral, sendo que um fator mais importante para corrida ao senado parece ser uma percepção priori da qualidade do candidato.

Knowledge disclosure as a weapon in technological change battles: straight shot or backfire?

This work aims at evaluating how effective is knowledge disclosure in attenuating institutional negative reactions caused by uncertainties brought by firms’ new strategies that respond to novel technologies. The empirical setting is from an era of technological ferment, the period of the introduction of the voice over internet protocol (VoIP) in the USA in the early 2000’s. This technology led to the convergence of the wireline telecommu- nications and cable television industries. The Institutional Brokers’ Estimate System (also known as the I/B/E/S system) was used to capture reactions of securities analysts, a revealed important source of institutional pressure on firms’ strategies. For assessing knowledge disclosure, a coding technique and a established content analysis framework were used to quantitatively measure the non-numerical and unstructured data of transcripts of business events occurred at that time. Eventually, several binary response models were tested in order to assess the effect of knowledge disclosure on the probability of institutional positive reactions. The findings are that the odds of favorable institutional reactions increase when a specific kind of knowledge is disclosed. It can be concluded that knowledge disclosure can be considered as a weapon in technological changes situations, attenuating adverse institutional reactions to the companies’ strategies in environments of technological changes.

A high-throughput screening assay for distinguishing nitrile hydratases from nitrilases

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A Neuromonitoring Approach to Facial Nerve Preservation During Image-guided Robotic Cochlear Implantation.

HYPOTHESIS A multielectrode probe in combination with an optimized stimulation protocol could provide sufficient sensitivity and specificity to act as an effective safety mechanism for preservation of the facial nerve in case of an unsafe drill distance during image-guided cochlear implantation. BACKGROUND A minimally invasive cochlear implantation is enabled by image-guided and robotic-assisted drilling of an access tunnel to the middle ear cavity. The approach requires the drill to pass at distances below 1 mm from the facial nerve and thus safety mechanisms for protecting this critical structure are required. Neuromonitoring is currently used to determine facial nerve proximity in mastoidectomy but lacks sensitivity and specificity necessaries to effectively distinguish the close distance ranges experienced in the minimally invasive approach, possibly because of current shunting of uninsulated stimulating drilling tools in the drill tunnel and because of nonoptimized stimulation parameters. To this end, we propose an advanced neuromonitoring approach using varying levels of stimulation parameters together with an integrated bipolar and monopolar stimulating probe. MATERIALS AND METHODS An in vivo study (sheep model) was conducted in which measurements at specifically planned and navigated lateral distances from the facial nerve were performed to determine if specific sets of stimulation parameters in combination with the proposed neuromonitoring system could reliably detect an imminent collision with the facial nerve. For the accurate positioning of the neuromonitoring probe, a dedicated robotic system for image-guided cochlear implantation was used and drilling accuracy was corrected on postoperative microcomputed tomographic images. RESULTS From 29 trajectories analyzed in five different subjects, a correlation between stimulus threshold and drill-to-facial nerve distance was found in trajectories colliding with the facial nerve (distance <0.1 mm). The shortest pulse duration that provided the highest linear correlation between stimulation intensity and drill-to-facial nerve distance was 250 μs. Only at low stimulus intensity values (≤0.3 mA) and with the bipolar configurations of the probe did the neuromonitoring system enable sufficient lateral specificity (>95%) at distances to the facial nerve below 0.5 mm. However, reduction in stimulus threshold to 0.3 mA or lower resulted in a decrease of facial nerve distance detection range below 0.1 mm (>95% sensitivity). Subsequent histopathology follow-up of three representative cases where the neuromonitoring system could reliably detect a collision with the facial nerve (distance <0.1 mm) revealed either mild or inexistent damage to the nerve fascicles. CONCLUSION Our findings suggest that although no general correlation between facial nerve distance and stimulation threshold existed, possibly because of variances in patient-specific anatomy, correlations at very close distances to the facial nerve and high levels of specificity would enable a binary response warning system to be developed using the proposed probe at low stimulation currents.

Reliability measures for local nodes assessment in classification trees

Most of the modem developments with classification trees are aimed at improving their predictive capacity. This article considers a curiously neglected aspect of classification trees, namely the reliability of predictions that come from a given classification tree. In the sense that a node of a tree represents a point in the predictor space in the limit, the aim of this article is the development of localized assessment of the reliability of prediction rules. A classification tree may be used either to provide a probability forecast, where for each node the membership probabilities for each class constitutes the prediction, or a true classification where each new observation is predictively assigned to a unique class. Correspondingly, two types of reliability measure will be derived-namely, prediction reliability and classification reliability. We use bootstrapping methods as the main tool to construct these measures. We also provide a suite of graphical displays by which they may be easily appreciated. In addition to providing some estimate of the reliability of specific forecasts of each type, these measures can also be used to guide future data collection to improve the effectiveness of the tree model. The motivating example we give has a binary response, namely the presence or absence of a species of Eucalypt, Eucalyptus cloeziana, at a given sampling location in response to a suite of environmental covariates, (although the methods are not restricted to binary response data).

Designs for generalized linear models with several variables and model uncertainty

Standard factorial designs sometimes may be inadequate for experiments that aim to estimate a generalized linear model, for example, for describing a binary response in terms of several variables. A method is proposed for finding exact designs for such experiments that uses a criterion allowing for uncertainty in the link function, the linear predictor, or the model parameters, together with a design search. Designs are assessed and compared by simulation of the distribution of efficiencies relative to locally optimal designs over a space of possible models. Exact designs are investigated for two applications, and their advantages over factorial and central composite designs are demonstrated.

Optimal crossover designs for logistic regression models in pharmacodynamics

Pharmacodynamics (PD) is the study of the biochemical and physiological effects of drugs. The construction of optimal designs for dose-ranging trials with multiple periods is considered in this paper, where the outcome of the trial (the effect of the drug) is considered to be a binary response: the success or failure of a drug to bring about a particular change in the subject after a given amount of time. The carryover effect of each dose from one period to the next is assumed to be proportional to the direct effect. It is shown for a logistic regression model that the efficiency of optimal parallel (single-period) or crossover (two-period) design is substantially greater than a balanced design. The optimal designs are also shown to be robust to misspecification of the value of the parameters. Finally, the parallel and crossover designs are combined to provide the experimenter with greater flexibility.