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Alternative Assumptions (alternative + assumption)
Selected AbstractsThe flight speed of parent birds feeding youngJOURNAL OF AVIAN BIOLOGY, Issue 6 2006Alasdair I. Houston I review previous models of the speed at which parent birds should fly when delivering food to their young. Norberg gives a graphical method of finding a parent's best flight speed. This speed maximizes the overall rate at which energy is delivered to the young. An alternative assumption is that a parent maximizes the net rate of delivery of energy. I suggest that in general we cannot distinguish between net rate and overall rate on the basis of whether the parent feeds itself. The best way to distinguish between these currencies may be to use qualitative predictions. I present new results on the effect of a constraint on energy expenditure on the parent's optimal speed. I show that the optimal speed when foraging should be less than the optimal speed when traveling. I also analyse the advantage to a parent of flying faster than the maximum range speed and evaluate previous empirical studies of the speed at which parent birds fly. Only one study claims that parent birds fly at the speed identified by Norberg, but I raise doubts about this claim. [source] Dividend payments in the classical risk model under absolute ruin with debit interestAPPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 3 2009Chunwei Wang Abstract This paper attempts to study the dividend payments in a compound Poisson surplus process with debit interest. Dividends are paid to the shareholders according to a barrier strategy. An alternative assumption is that business can go on after ruin, as long as it is profitable. When the surplus is negative, a debit interest is applied. At first, we obtain the integro-differential equations satisfied by the moment-generating function and moments of the discounted dividend payments and we also prove the continuous property of them at zero. Then, applying these results, we get the explicit expressions of the moment-generating function and moments of the discounted dividend payments for exponential claims. Furthermore, we discuss the optimal dividend barrier when the claim sizes have a common exponential distribution. Finally, we give the numerical examples for exponential claims and Erlang (2) claims. Copyright © 2008 John Wiley & Sons, Ltd. [source] Estimating uncertainty in fish stock assessment and forecastingFISH AND FISHERIES, Issue 2 2001Kenneth Patterson Abstract A variety of tools are available to quantify uncertainty in age-structured fish stock assessments and in management forecasts. These tools are based on particular choices for the underlying population dynamics model, the aspects of the assessment considered uncertain, and the approach for assessing uncertainty (Bayes, frequentist or likelihood). The current state of the art is advancing rapidly as a consequence of the availability of increased computational power, but there remains little consistency in the choices made for assessments and forecasts. This can be explained by several factors including the specifics of the species under consideration, the purpose for which the analysis is conducted and the institutional framework within which the methods are developed and used, including the availability and customary usage of software tools. Little testing of either the methods or their assumptions has yet been done. Thus, it is not possible to argue either that the methods perform well or perform poorly or that any particular conditioning choices are more appropriate in general terms than others. Despite much recent progress, fisheries science has yet to identify a means for identifying appropriate conditioning choices such that the probability distributions which are calculated for management purposes do adequately represent the probabilities of eventual real outcomes. Therefore, we conclude that increased focus should be placed on testing and carefully examining the choices made when conducting these analyses, and that more attention must be given to examining the sensitivity to alternative assumptions and model structures. Provision of advice concerning uncertainty in stock assessments should include consideration of such sensitivities, and should use model-averaging methods, decision tables or management procedure simulations in cases where advice is strongly sensitive to model assumptions. [source] Forecasting financial volatility of the Athens stock exchange daily returns: an application of the asymmetric normal mixture GARCH modelINTERNATIONAL JOURNAL OF FINANCE & ECONOMICS, Issue 4 2010Anastassios A. Drakos Abstract In this paper we model the return volatility of stocks traded in the Athens Stock Exchange using alternative GARCH models. We employ daily data for the period January 1998 to November 2008 allowing us to capture possible positive and negative effects that may be due to either contagion or idiosyncratic sources. The econometric analysis is based on the estimation of a class of five GARCH models under alternative assumptions with respect to the error distribution. The main findings of our analysis are: first, based on a battery of diagnostic tests it is shown that the normal mixture asymmetric GARCH (NM-AGARCH) models perform better in modeling the volatility of stock returns. Second, it is shown that with the use of the Kupiec's tests for in-sample and out-of-sample forecasting performance the evidence is mixed as the choice of the appropriate volatility model depends on the trading position under consideration. Third, at the 99% confidence interval the NM-AGARCH model with skewed Student-distribution outperforms all other competing models both for in-sample and out-of-sample forecasting performance. This increase in predictive performance for higher confidence intervals of the NM-AGARCH model with skewed Student-distribution makes this specification consistent with the requirements of the Basel II agreement. Copyright © 2010 John Wiley & Sons, Ltd. [source] OPTIMAL DISCOUNTING IN CONTROL PROBLEMS THAT SPAN MULTIPLE GENERATIONSNATURAL RESOURCE MODELING, Issue 3 2005FRANK CALIENDO ABSTRACT. The principal contribution of this paper is the linking together of separate control problems across multiple generations using the bequest motive, intergenerational altruism, rational expectations, and solution boundary conditions. We demonstrate that discounting at the market rate of interest is an endogenous characteristic of a general equilibrium, optimal control problem that spans multiple generations. Within the confines of our model, we prove that it is optimal to discount at the market rate of interest the social benefits to distant generations from immediate clean up at toxic waste sites if the current generation that bears the cleanup cost is perfectly altruistic towards future generations. Also, we show that this result holds for alternative assumptions regarding pure time preference. Moreover, the result holds regardless of whether selfish interim generations attempt to undo the provisions made for distant generations. In our distortion-free deterministic model, the evidence for intergenerational discounting at the market rate of interest is compelling. [source] Estimates of Pregnancies Averted Through California's Family Planning Waiver Program in 2002PERSPECTIVES ON SEXUAL AND REPRODUCTIVE HEALTH, Issue 3 2006Diana Greene Foster CONTEXT: During its first year of operation (1997-1998), California's family planning program, Family PACT, helped more than 750,000 clients to avert an estimated 108,000 pregnancies. Given subsequent increases in the numbers of clients served and contraceptive methods offered by the program, updated estimates of its impact on fertility are needed. METHODS: Claims data on contraceptives dispensed were used to estimate the number of pregnancies experienced by women in the program in 2002. Medical record data on methods used prior to enrollment were used to predict client fertility in the absence of the program. Further analyses examined the sensitivity of these estimates to alternative assumptions about contraceptive failure rates, contraceptive continuation and contraceptive use in the absence of program services. RESULTS: Almost 6.4 million woman-months of contraception, provided primarily by oral contraceptives (57%), barrier methods (19%) and the injectable (18%), were dispensed through Family PACT during 2002. As a result, an estimated 205,000 pregnancies,which would have resulted in 79,000 abortions and 94,000 births, including 21,400 births to adolescents,were averted. Changing the base assumptions regarding contraceptive failure rates or method use had relatively small effects on the estimates, whereas assuming that clients would use no contraceptives in the absence of Family PACT nearly tripled the estimate of pregnancies averted. CONCLUSIONS: Because all contraceptive methods substantially reduce the risk of pregnancy, Family PACT'S impact on preventing pregnancy lies primarily in providing contraceptives to women who would otherwise not use any method. [source] Working memory interference during processing texts and pictures: Implications for the explanation of the modality effectAPPLIED COGNITIVE PSYCHOLOGY, Issue 2 2010Ralf Rummer Auditory text presentation improves learning with pictures and texts. With sequential text,picture presentation, cognitive models of multimedia learning explain this modality effect in terms of greater visuo-spatial working memory load with visual as compared to auditory texts. Visual texts are assumed to demand the same working memory subsystem as pictures, while auditory texts make use of an additional cognitive resource. We provide two alternative assumptions that relate to more basic processes: First, acoustic-sensory information causes a retention advantage for auditory over visual texts which occurs no matter if a picture is presented or not. Second, eye movements during reading hamper visuo-spatial rehearsal. Two experiments applying elementary procedures provide first evidence for these assumptions. Experiment 1 demonstrates that, regarding text recall, the auditory advantage is independent of visuo-spatial working memory load. Experiment 2 reveals worse matrix recognition performance after reading text requiring eye movements than after listening or reading without eye movements. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structure of Firm Location Choices: An Examination of Japanese Greenfield Investment in China,ASIAN ECONOMIC JOURNAL, Issue 1 2007Shaoming Cheng F21; L20; R30 This paper presents an empirical investigation of the location decision structure of Japanese investors in China. In this study, a nested logit model and rich Japanese firm-level greenfield manufacturing foreign direct investment data are calibrated together. This examination is not only driven by the unsatisfactory model specification of the conditional logit model in previous location choice analyses, specifically the violation of the independence from irrelevant alternatives assumption; but is also driven by the urgent need to better understand foreign investors' in general and Japanese investors' in particular location decision structure in China. Two potential hierarchical and sequential location decision-making structures of Japanese investors are then tested, which are respectively in line with the spatial divide of China's FDI preferential policies and with China's six traditional census areas. [source] | |||||||||||||