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1.
Copulas provide an attractive approach to the construction of multivariate distributions with flexible marginal distributions and different forms of dependences. Of particular importance in many areas is the possibility of forecasting the tail-dependences explicitly. Most of the available approaches are only able to estimate tail-dependences and correlations via nuisance parameters, and cannot be used for either interpretation or forecasting. We propose a general Bayesian approach for modeling and forecasting tail-dependences and correlations as explicit functions of covariates, with the aim of improving the copula forecasting performance. The proposed covariate-dependent copula model also allows for Bayesian variable selection from among the covariates of the marginal models, as well as the copula density. The copulas that we study include the Joe-Clayton copula, the Clayton copula, the Gumbel copula and the Student’s t-copula. Posterior inference is carried out using an efficient MCMC simulation method. Our approach is applied to both simulated data and the S&P 100 and S&P 600 stock indices. The forecasting performance of the proposed approach is compared with those of other modeling strategies based on log predictive scores. A value-at-risk evaluation is also performed for the model comparisons.  相似文献   

2.
The random coefficients multinomial choice logit model, also known as the mixed logit, has been widely used in empirical choice analysis for the last thirty years. We prove that the distribution of random coefficients in the multinomial logit model is nonparametrically identified. Our approach requires variation in product characteristics only locally and does not rely on the special regressors with large supports used in related papers. One of our two identification arguments is constructive. Both approaches may be applied to other choice models with random coefficients.  相似文献   

3.
A special characteristic of the patent system is that it features multiple patent-policy levers that can be employed by policymakers. In this note, we develop an R&D-based growth model to analyze the optimal mix of patent instruments by considering patent breadth and the division of profit in research joint ventures. Our results are as follows. First, we analytically derive the optimal mix of patent breadth and the profit-division rule. Then, we calibrate the model to quantitatively evaluate the welfare gain from optimizing both patent instruments versus optimizing only patent breadth. We find that the welfare gain can be quantitatively significant.  相似文献   

4.
For a multilevel model with two levels and only a random intercept, the quality of different estimators of the random intercept is examined. Analytical results are given for the marginal model interpretation where negative estimates of the variance components are allowed for. Except for four or five level-2 units, the Empirical Bayes Estimator (EBE) has a lower average Bayes risk than the Ordinary Least Squares Estimator (OLSE). The EBEs based on restricted maximum likelihood (REML) estimators of the variance components have a lower Bayes risk than the EBEs based on maximum likelihood (ML) estimators. For the hierarchical model interpretation, where estimates of the variance components are restricted being positive, Monte Carlo simulations were done. In this case the EBE has a lower average Bayes risk than the OLSE, also for four or five level-2 units. For large numbers of level-1 (30) or level-2 units (100), the performances of REML-based and ML-based EBEs are comparable. For small numbers of level-1 (10) and level-2 units (25), the REML-based EBEs have a lower Bayes risk than ML-based EBEs only for high intraclass correlations (0.5).  相似文献   

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In this paper we introduce a class of tentatively plausible, fixed-coefficient models of money demand and evaluate their forecast performance. When these models are reestimated allowing all coefficients to vary over time, the forecasting performance improves dramatically. Aside from offering insights about improved methods of analyzing time series data, the most promising direct use for point estimates derived from time-varying coefficients is as an aid in calibrating proposed models of the kind discussed here.  相似文献   

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Most contemporary total quality management (TQM) practice is influenced, directly or indirectly, by structured, acontextual and standardized quality models. The present paper focuses on the strategic introduction of one such model, namely the Swedish Institute for Quality (SIQ) model for performance excellence, in a Swedish public-sector organization, which we refer to as ‘the Authority.’ We take our theoretical stance from Foucault's concept of ‘power/knowledge.’ In describing the case, we focus on the management team of one of the Authority's ten regions. Our analysis shows the members of the management team using the SIQ model to objectify both the organization and themselves as managers. However, contrary to many critical or managerial accounts, the SIQ model was not totalizing: management subjectivities changed but were not entirely reconstituted, and some resistance to them was generated by the members of the management team, in their role as professionals.  相似文献   

9.
Air transportation plays a crucial role in the agile and dynamic environment of contemporary supply chains. This industry is characterised by high air cargo demand uncertainty, making forecasting extremely challenging. An in-depth case study has been undertaken in order to explore and untangle the factors influencing demand forecasting and consequently to improve the operational performance of an air cargo handling company. It has been identified that in practice, the demand forecasting process does not provide the necessary level of accuracy, to effectively cope with the high demand uncertainty. This has a negative impact on a whole range of air cargo operations, but especially on the management of the workforce, which is the most expensive resource in the air cargo handling industry. Besides forecast inaccuracy, a range of additional hidden factors that affect operations management have been identified. A number of recommendations have been made to improve demand forecasting and workforce management.  相似文献   

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In general, the construction of optimal designs is apparently a difficult task for the approximation of a random field indexed by more than one dimension. Besides the rate of convergence of the minimum achievable error hardly anything is known until now. However, if there is an immanent structure present in the random field, then, taking this structure into account, improved estimates can be obtained. For this situation we present adequate designs which show, at least, a nearly optimal performance. work supported by 313/ARC/VII/93/151 of the DAAD work supported by Ku719/2-1 of the DFG  相似文献   

12.
Errors of measurement have long been recognized as a chronic problem in statistical analysis. Although there is a vast statistical literature of multiple regression models estimating the air pollution-mortality relationship, this problem has been largely ignored. It is well known that pollution measures contain error, but the consequences of this error for regression estimates is not known. We use Lave and Seskin's air pollution model to demonstrate the consequences of random measurement error. We assume a range of 0% to 50% of the variance of the pollution measures is due to error. We find large differences in the estimated effects on mortality of the pollution variables as well as the other explanatory variables once this measurement error is taken into account. These results cast doubt on the usual regression estimates of the mortality effects of air pollution. More generally our results demonstrate the consequences of random measurement error in the explanatory variable of a multiple regression analysis and the misleading conclusions that may result in policy research if this error is ignored.  相似文献   

13.
For random elements X and Y (e.g. vectors) a complete characterization of their association is given in terms of an odds ratio function. The main result establishes for any odds ratio function and any pre-specified marginals the unique existence of a corresponding joint distribution (the joint density is obtained as a limit of an iterative procedure of marginal fittings). Restricting only the odds ratio function but not the marginals leads to semi-parmetric association models for which statistical inference is available for samples drawn conditionally on either X or Y. Log-bilinear association models for random vectors X and Y are introduced which generalize standard (regression) models by removing restrictions on the marginals. In particular, the logistic regression model is recognized as a log-bilinear association model. And the joint distribution of X and Y is shown to be multivariate normal if and only if both marginals are normal and the association is log-bilinear.Acknowledgements The author thanks both referees for their helpful comments which improved the first draft of the paper.  相似文献   

14.
《Journal of econometrics》1987,36(3):383-389
Iterated GLS has a remarkable property when applied to the random effects model in its usual parameterization. The values for the parameter that measures relative variance, obtained through successive iterations, form a monotonic sequence. This property provides convenient checks for multiple maxima of the likelihood function and for existence of a local maximum that satisfies the non-negativity condition.  相似文献   

15.
In the past two decades, academics and practitioners have attempted to improve understanding of environmental management by classifying companies' environmental behaviour, and evaluating their performance. Driven by both research and societal interest, this has resulted in a wave of stage or phase models, and a range of typologies. This article gives an overview of the development of such environmental management models, analysing their characteristics, strengths and weaknesses. An evolution can be noted in the direction of typologies and non‐linear models to deal with organizational and strategic complexities. Models are starting to pay more attention to the management side. To overcome problems of operationalization and limited company and sector specificity, environmental performance evaluation systems have emerged more recently. Although comprehensive performance assessments are still unavailable, the tenets of such a system can already be delineated. The paper presents these components, and draws conclusions on the contribution of environmental management models and performance evaluation systems. Copyright © 2002 John Wiley & Sons, Ltd. and ERP Environment  相似文献   

16.

This paper assesses the options available to researchers analysing multilevel (including longitudinal) data, with the aim of supporting good methodological decision-making. Given the confusion in the literature about the key properties of fixed and random effects (FE and RE) models, we present these models’ capabilities and limitations. We also discuss the within-between RE model, sometimes misleadingly labelled a ‘hybrid’ model, showing that it is the most general of the three, with all the strengths of the other two. As such, and because it allows for important extensions—notably random slopes—we argue it should be used (as a starting point at least) in all multilevel analyses. We develop the argument through simulations, evaluating how these models cope with some likely mis-specifications. These simulations reveal that (1) failing to include random slopes can generate anti-conservative standard errors, and (2) assuming random intercepts are Normally distributed, when they are not, introduces only modest biases. These results strengthen the case for the use of, and need for, these models.

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We consider utility functions defined on P?, the closure of the positive orthant of Rl, that satisfy the differentiable monotonicity and differentiable convexity conditions. We show that the demand function derived from such a utility function is piecewise smooth in a strong sense. We use this result to show that the Pareto optimal subset of a pure exchange economy derived from the kind of utility functions we consider is generically the union of a finite number of compact manifolds-with-corners.  相似文献   

19.
Supply chain process variability is the level of inconsistency, or volatility, in the flow of goods into, through, and out of a firm. The research investigates the links among organizational structure (formalization and integration), supply chain process variability, and performance as moderated by environmental uncertainty. We found that in a predictable demand environment, only formal control affects supply chain process variability, leading to improved financial results; but in an unpredictable demand environment, only cross-functional integration affects supply chain process variability, leading to improved financial performance. We also examined whether supply chain process variability is a complete or partial mediator of the relationship between organizational structure and performance, and found that: (1) in a predictable demand environment, supply chain process variability completely mediates the relationship between formal control and performance and (2) in an unpredictable demand environment, supply chain process variability partially mediates the relationship between integration and performance. Supply chain process variability has an inverse relationship with financial performance, regardless of the demand environment; and organizational structure provides managers with the mechanisms to mitigate this variability's detrimental impact on financial performance.  相似文献   

20.
We compare a number of methods that have been proposed in the literature for obtaining h-step ahead minimum mean square error forecasts for self-exciting threshold autoregressive (SETAR) models. These forecasts are compared to those from an AR model. The comparison of forecasting methods is made using Monte Carlo simulation. The Monte-Carlo method of calculating SETAR forecasts is generally at least as good as that of the other methods we consider. An exception is when the disturbances in the SETAR model come from a highly asymmetric distribution, when a Bootstrap method is to be preferred.An empirical application calculates multi-period forecasts from a SETAR model of US gross national product using a number of the forecasting methods. We find that whether there are improvements in forecast performance relative to a linear AR model depends on the historical epoch we select, and whether forecasts are evaluated conditional on the regime the process was in at the time the forecast was made.  相似文献   

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