Model selection in neural networks

In this article we examine how model selection in neural networks can be guided by statistical procedures such as hypotheses tests, information criteria and cross validation. The application of these methods in neural network models is discussed, paying attention especially to the identification problems encountered. We then propose five specification strategies based on different statistical procedures and compare them in a simulation study. As the results of the study are promising, it is suggested that a statistical analysis should become an integral part of neural network modelling. --Neural Networks,Statistical Inference,Model Selection,Identification,Information Criteria,Cross Validation

The economics of a stage-structured wildlife population model

A four-stage model (calves, yearlings, adult female and adult male) of the Scandinavian moose (Alces alces) is formulated. Fecundity is density dependent while mortality is density independent. The paper aims to demonstrate the economic content of such a wildlife model and how this content may change under shifting economic and ecological conditions. Two different harvesting regimes are explored: hunting for meat, and trophy hunting. It is shown how different ways to compose the harvest influences the profitability while, at the same time, the population levels of the different stages may only change modestly. It is also shown why different market situations require different compositions of the harvest, knowledge that is disregarded in the traditional bioeconomic modelling approach.wildlife; harvesting; trophy hunting

A Bioeconomic Analysis of a Wild Atlantic Salmon (Salmo salar) Recreational Fishery

A biomass model of a wild salmon (Salmo salar) river recreational fishery is formulated, and the ways in which economic and biological conditions influence harvesting, stock size, profitability, and the benefit of the anglers are studied. The demand for recreational angling is met by fishing permits supplied by myopic profit-maximizing landowners. Both price-taking and monopolistic supply is studied. These schemes are contrasted with an overall river management regime. Gear regulations in the recreational fishery, but also the commercial fishery, are analysed under the various management scenarios, and the paper concludes with some policy implications. One novel result is that imposing gear restrictions in the recreational fishery may have the exact opposite stock effects of imposing restrictions on the marine harvest.Salmon, recreational fishery, conflicting interests, stock dynamics., Demand and Price Analysis, Environmental Economics and Policy, Research Methods/ Statistical Methods, Q26, Q22, Q21.,

Managing a Migratory Species that is both a Value and Pest

Wild animals can represent both value and nuisance. We consider the moose (Alces alces), which due to seasonal migration causes browsing damage in some areas while creating hunting value in other areas. We first explore a situation when harvesting, following today’s practice in Norway, only takes place in the fall. Next, the season is extended to include winter harvesting. It is shown how this redistributes harvesting benefits between areas and landowners, and under which conditions total net benefit increases. The model is illustrated by a real life example from the Swe-Nor moose region some 250 kilometers north of Oslo, Norway.

Improving the pricing of options: a neural network approach

In this paper we apply statistical inference techniques to build neural network models which are able to explain the prices of call options written on the German stock index DAX. By testing for the explanatory power of several input variables serving as network inputs, some insight into the pricing process of the option market is obtained. The results indicate that statistical specification strategies lead to parsimonious networks which have a superior out-of-sample performance when compared to the Black/Scholes model. We further validate our results by providing plausible hedge parameters. --Option Pricing,Neural Networks,Statistical Inference,Model Selection

When a Fish is a Fish: The Economic Impacts of Escaped Farmed Fish

The escape of cultured fish from a marine aquaculture facility is a type of biological invasion that may lead to a variety of potential ecological and economic effects on native fish. This paper develops a general invasive species impact model to capture explicitly both the ecological and economic effects of invasive species, especially escaped farmed fish, on native stocks and harvests. First, the possible effects of escaped farmed fish on the growth and stock size of a native fish are examined. Next, a bioeconomic model to analyze changes in yield, benefit distribution, and overall profitability is constructed. Different harvesting scenarios, such as commercial, recreational, and joint commercial and recreational fishing, are explored. The model is illustrated by a case study of the interaction between native and farmed Atlantic salmon in Norway. The results suggest that both the harvest and profitability of a native fish stock may decline after an invasion, but the total profits from the harvest of both native and farmed stocks may increase or decrease, depending on the strength of the ecological and economic parameters.

Model selection in neural networks

In this article we examine how model selection in neural networks can be guided by statistical procedures such as hypotheses tests, information criteria and cross validation. The application of these methods in neural network models is discussed, paying attention especially to the identification problems encountered. We then propose five specification strategies based on different statistical procedures and compare them in a simulation study. As the results of the study are promising, it is suggested that a statistical analysis should become an integral part of neural network modelling

Transition and Justice: An Introduction

Since the end of the Cold War, political new beginnings have increasingly been linked to questions of transitional justice. The contributions to this collection examine a series of cases from across the African continent where peaceful ‘new beginnings’ have been declared after periods of violence and where transitional justice institutions played a role in defining justice and the new socio-political order. Three issues seem to be crucial to the understanding of transitional justice in the context of wider social debates on justice and political change: the problem of ‘new beginnings’, of finding a foundation for that which explicitly breaks with the past; the discrepancies between lofty promises and the messy realities of transitional justice in action; and the dialectic between logics of the exception and the ordinary, employed to legitimize or resist transitional justice mechanisms. These are the particular focus of this Introduction

Improving the pricing of options: a neural network approach

In this paper we apply statistical inference techniques to build neural network models which are able to explain the prices of call options written on the German stock index DAX. By testing for the explanatory power of several input variables serving as network inputs, some insight into the pricing process of the option market is obtained. The results indicate that statistical specification strategies lead to parsimonious networks which have a superior out-of-sample performance when compared to the Black/Scholes model. We further validate our results by providing plausible hedge parameters

Studies and perspectives of plasminogen activators

The fibrinolytic system participates in a variety of physiological and pathological processes. It consists of an inactive proenzyme, plasminogen, which can be activated to the active serine protease plasmin by the action of different types of plasminogen activators. The main function of the fibrinolytic system is to dissolve fibrin deposits in blood vessels. Thrombogenesis can be influenced by an insufficient or ineffective fibrinolytic system. The tissue-type plasminogen activator (t-PA) receives considerable attention since its deficiency has been shown to be a leading cause for thrombophilic situations. Increases of its main inhibitor (PAI) probably play a similar role. Using the advantages of recombinant DNA technology modem thrombolytic drugs based on the structure of plasminogen activators are applied for the therapy of thromboembolic diseases. Structure and function of the fibrinolytic system are outlined in the following review. Diagnostic evaluation of the fibrinolytic system and therapeutic considerations are discussed.Biomedical Reviews 1992; 1: 33-38