C.S. Bos (Charles)
http://repub.eur.nl/ppl/1508/
List of Publicationsenhttp://repub.eur.nl/eur_logo.png
http://repub.eur.nl/
RePub, Erasmus University RepositoryAdjunctive treatment of keloids: Comparison of photodynamic therapy with brachytherapy
http://repub.eur.nl/pub/62745/
Wed, 01 May 2013 00:00:01 GMT<div>C.S. Bos</div><div>R. Mehilal</div><div>A. Al-Mamgani</div><div>P.H. van Rooij</div><div>A. Bhawanie</div><div>H.J.C.M. Sterenborg</div><div>R.T.J. Wai</div><div>M.A.M. Mureau</div><div>D.J. Robinson</div><div>P.C. Levendag</div>
Background: The aesthetic result after brachytherapy, especially hypopigmentation, remains a significant problem. Given that brachytherapy may be carcinogenic, it is difficult to recommend this treatment in young patients. For these reasons, there is a need for alternatives to radiation. Methods: The purpose of this study was to evaluate the effectiveness of adjuvant photodynamic therapy (PDT) using aminolevulinic acid after keloid excision and to compare it to keloid excision followed by brachytherapy. To assess outcome, the Patient and Observer Scar Assessment Scale (POSAS) was used. Results: Thirty-four patients treated for 45 keloids were evaluated. Twenty-two patients (27 lesions) received brachytherapy and 12 (18 lesions) received PDT. The observers scored a mean POSAS of 19.1 (range 13.0-34.0) for brachytherapy and 24.6 (range 11.0-37.0) for PDT (p = 0.005). The independent observers scored a mean POSAS of 14.6 (range 10.0-20.0) for brachytherapy and 18.6 (range 9.0-42.0) for PDT (p = 0.018). The patients reported a significantly better mean POSAS score after brachytherapy (22.8, range 7.0-53.0) than following PDT (34.2, range 11.0-63.0). The patients' POSAS score showed no significant difference for the item "general impression" for both treatment groups; the observers scored significantly higher for PDT treatment. The independent observers revealed a higher score for general impression after PDT although not reaching significance. Conclusions: Patients and observers appear to be more satisfied with the results after brachytherapy than PDT. However, patients still have a positive general impression after PDT. Adjunctive aminolevulinic acid-PDT for the treatment of keloids could be used as an alternative for brachytherapy. Level of Evidence: Level IV, therapeutic study.Adaptive radial-based direction sampling: some flexible and robust Monte Carlo integration methods
http://repub.eur.nl/pub/11191/
Wed, 01 Dec 2004 00:00:01 GMT<div>L. Bauwens</div><div>C.S. Bos</div><div>H.K. van Dijk</div><div>R.D. van Oest</div>
Adaptive radial-based direction sampling (ARDS) algorithms are specified for Bayesian analysis of models with non-elliptical, possibly, multimodal target distributions. A key step is a radial-based transformation to directions and distances. After the transformation a Metropolis-Hastings method or, alternatively, an importance sampling method is applied to evaluate generated directions. Next, distances are generated from the exact target distribution. An adaptive procedure is applied to update the initial location and covariance matrix in order to sample directions in an efficient way. The ARDS algorithms are illustrated on a regression model with scale contamination and a mixture model for economic growth of the USA.Explaining Adaptive Radial-Based Direction Sampling
http://repub.eur.nl/pub/1045/
Thu, 07 Aug 2003 00:00:01 GMT<div>L. Bauwens</div><div>C.S. Bos</div><div>H.K. van Dijk</div><div>R.D. van Oest</div>
In this short paper we summarize the computational steps of Adaptive Radial-Based Direction Sampling (ARDS), which can be used for Bayesian analysis of ill behaved target densities. We consider one simulation experiment in order to illustrate the good performance of ARDS relative to the independence chain MH algorithm and importance sampling.Adaptive radial-based direction sampling; Some flexible and robust Monte Carlo integration methods
http://repub.eur.nl/pub/1722/
Wed, 06 Aug 2003 00:00:01 GMT<div>L. Bauwens</div><div>C.S. Bos</div><div>H.K. van Dijk</div><div>R.D. van Oest</div>
Adaptive radial-based direction sampling (ARDS) algorithms are specified for Bayesian analysis of models with nonelliptical, possibly, multimodal target distributions.
A key step is a radial-based transformation to directions and distances. After the transformations a Metropolis-Hastings method or, alternatively, an importance sampling method is applied to evaluate generated directions. Next, distances are generated from the exact target distribution by means of the numerical inverse transformation method. An adaptive procedure is applied to update the initial location and covariance matrix in order to sample directions in an efficient way. Tested on a set of canonical mixture models that feature multimodality, strong correlation, and skewness, the ARDS algorithms compare favourably with the standard Metropolis-Hastings and importance samplers in terms of flexibility and robustness. The empirical examples include a regression model with scale contamination and a mixture model for economic growth of the USA.Adaptive polar sampling, a class of flexibel and robust Monte Carlo integration methods
http://repub.eur.nl/pub/555/
Tue, 17 Sep 2002 00:00:01 GMT<div>L. Bauwens</div><div>C.S. Bos</div><div>H.K. van Dijk</div><div>R.D. van Oest</div>
Adaptive Polar Sampling (APS) algorithms are proposed for Bayesian analysis of models with
nonelliptical, possibly, multimodal posterior distributions. A location-scale transformation
and a transformation to polar coordinates are used. After the transformation to polar
coordinates, a Metropolis-Hastings method or, alternatively, an importance sampling
method is applied to sample directions and, conditionally on these, distances are
generated by inverting the cumulative distribution function. A sequential procedure is
applied to update the initial location and scaling matrix in order to sample directions
in an efficient way. Tested on a set of canonical mixture models that feature multimodality,
strong correlation, and skewness, the APS algorithms compare favourably with the standard
Metropolis-Hastings and importance samplers in terms of flexibility and robustness. APS is
applied to several econometric and statistical examples. The empirical results for a
regression model with scale contamination, an ARMA-GARCH-Student t model with near
cancellation of roots and heavy tails, a mixture model for economic growth, and a
nonlinear threshold model for industrial production growth confirm the practical
flexibility and robustness of APS.Inflation, forecast intervals and long memory regression models
http://repub.eur.nl/pub/2162/
Tue, 16 Apr 2002 00:00:01 GMT<div>Ph.H.B.F. Franses</div><div>C.S. Bos</div><div>M. Ooms</div>
We examine recursive out-of-sample forecasting of monthly postwar US core inflation and log price levels. We use the autoregressive fractionally integrated moving average model with explanatory variables (ARFIMAX). Our analysis suggests a significant explanatory power of leading indicators associated with macroeconomic activity and monetary conditions for forecasting horizons up to 2 years. Correcting for the effect of explanatory variables, we still find fractional integration and structural breaks in the mean and variance of inflation in the 1970s and 1980s. We compare the forecasts of ARFIMAX models and ARIMAX models over the period 1984–1999. The ARIMAX(1, 1, 1) model provides the best forecasts, but its multi-step forecast intervals are too large. The multi-step forecast intervals of the ARFIMAX(0, d, 0) model prove to be more realistic.Time Varying Parameter Models for Inflation and Exchange Rates
http://repub.eur.nl/pub/1854/
Thu, 13 Sep 2001 00:00:01 GMT<div>C.S. Bos</div>
Een van de onderwerpen binnen de Econometrie is het zoeken naar de structuur die
schuil gaat achter macroeconomische reeksen. Dit proefschrift gaat in op twee van der
gelijke reeksen, namelijk inflatie en wisselkoers reeksen. Uiteraard zijn dergelijke reeksen
al vele malen geanalyseerd, met wisselend resultaat. In dit proefschrift wordt gepoogd
op nieuwe wijze de data te analyseren, waarbij speciaal aandacht is voor modellen met
tijdsvariÄerende parameters. Uit de gereedschapskist van de econometrie worden diverse
technieken tevoorschijn gehaald die de beste (lees: meest gedetailleerde, waarheidsgetrou
we) beschrijving beloven te leveren van de structuren die aan de in°atie en wisselkoers
reeksen ten grondslag liggen.
Hierna worden de diverse hoofdstukken, met hun conclusies, kort beschreven.Inflation, Forecast Intervals and Long Memory Regression Models
http://repub.eur.nl/pub/6874/
Fri, 23 Feb 2001 00:00:01 GMT<div>C.S. Bos</div><div>Ph.H.B.F. Franses</div><div>M. Ooms</div>
We examine recursive out-of-sample forecasting of monthly postwar U.S. core inflation and log price levels. We use the autoregressive fractionally integrated moving average model with explanatory variables (ARFIMAX). Our analysis suggests a significant explanatory power of leading indicators associated with macroeconomic activity and monetary conditions for forecasting horizons up to two years. Even after correcting for the effect of explanatory variables, there is conclusive evidence of both fractional integration and structural breaks in the mean and variance of inflation in the 1970s and 1980s and we incorporate these breaks in the forecasting model for the 1980s and 1990s. We compare the results of the fractionally integrated ARFIMA(0,d,0) model with those for ARIMA(1,d,1) models with fixed order of d=0 and d=1 for inflation. Comparing mean squared forecast errors, we find that the ARMA(1,1) model performs worse than the other models over our evaluation period 1984-1999. The ARIMA(1,1,1) model provides the best forecasts, but its multi-step forecast intervals are too large.On the Variation of Hedging Decisions in Daily Currency Risk Management
http://repub.eur.nl/pub/6877/
Thu, 08 Feb 2001 00:00:01 GMT<div>C.S. Bos</div><div>R.J. Mahieu</div><div>H.K. van Dijk</div>
Internationally operating firrns naturally face the decision whether or not to hedge the currency risk implied by foreign investments. In a recent paper, Bos, Mahieu and van Dijk (2000) evaluate the returns from optimal and alternative currency hedging strategies, for a series of 7 models, using Bayesian inference and decision analysis. The models differ in the way time-varying means, variances or the unconditional error distributions are incorporated. In this extension, we compare the hedging decisions and financial returns and utilities as they result from the modelling assumptions and the attitudes towards risk.Daily Exchange Rate Behaviour and Hedging of Currency Risk
http://repub.eur.nl/pub/6878/
Thu, 08 Feb 2001 00:00:01 GMT<div>C.S. Bos</div><div>R.J. Mahieu</div><div>H.K. van Dijk</div>
We construct models which enable a decision-maker to analyze the implications of typical time series patterns of daily exchange rates for currency risk management. Our approach is Bayesian where extensive use is made of Markov chain Monte Carlo methods. The effects of several model characteristics (unit roots, GARCH, stochastic volatility, heavy tailed disturbance densities) are investigated in relation to the hedging strategies. Consequently, we can make a distinction between statistical relevance of model specifications, and the economic consequences from a risk management point of view. We compute payoffs and utilities from several alternative hedge strategies. The results indicate that modelling time varying features of exchange rate returns may lead to improved hedge behaviour within currency overlay management.On the variation of hedging decisions in daily currency risk management
http://repub.eur.nl/pub/1653/
Thu, 09 Nov 2000 00:00:01 GMT<div>C.S. Bos</div><div>R.J. Mahieu</div><div>H.K. van Dijk</div>
Internationally operating firms naturally face the decision whether or not to hedge the currency risk implied by foreign investments. In a recent paper, Bos, Mahieu and van Dijk evaluate the returns from optimal and alternative currency hedging strategies, for a series of 7 models, using Bayesian inference and decision analysis. The models differ in the way time-varying means, variances or the unconditional error distributions are incorporated. In this extension, we compare the hedging decisions
and financial returns and utilities as they result from the modelling assumptions and the attitudes towards risk.Daily exchange rate behaviour and hedging of currency risk
http://repub.eur.nl/pub/1657/
Wed, 30 Aug 2000 00:00:01 GMT<div>C.S. Bos</div><div>R.J. Mahieu</div><div>H.K. van Dijk</div>
We construct models which enable a decision-maker to analyze the implications of typical time series patterns of daily exchange rates for currency risk management. Our approach is Bayesian where extensive use is made of Markov chain Monte Carlo methods. The effects of several model characteristics (unit roots, GARCH, stochastic volatility, heavy tailed disturbance densities) are investigated in relation to the
hedging strategies. Consequently, we can make a distinction between statistical relevance of model specifications, and the economic consequences from a risk management point of view. We compute payoffs from several alternative hedge strategies. These payoffs indicate that
modelling time-varying features of exchange rate returns may lead to improved hedge behaviour within currency overlay management.Daily exchange rate behaviour and hedging of currency risk
http://repub.eur.nl/pub/11335/
Sat, 01 Jan 2000 00:00:01 GMT<div>C.S. Bos</div><div>R.J. Mahieu</div><div>H.K. van Dijk</div>
We construct models which enable a decision maker to analyse the implications of typical time series patterns of daily exchange rates for currency risk management. Our approach is Bayesian where extensive use is made of Markov chain Monte Carlo methods. The effects of several model characteristics (unit roots, GARCH, stochastic volatility, heavy-tailed disturbance densities) are investigated in relation to the hedging strategies. Consequently, we can make a distinction between statistical relevance of model specifications and the economic consequences from a risk management point of view. We compute payoffs and utilities from several alternative hedge strategies. The results indicate that modelling time-varying features of exchange rate returns may lead to improved hedge behaviour within currency overlay management.Long memory and level shifts: re-analysing inflation rates
http://repub.eur.nl/pub/13508/
Thu, 11 Nov 1999 00:00:01 GMT<div>C.S. Bos</div><div>Ph.H.B.F. Franses</div><div>M. Ooms</div>
A key application of long memory time series models concerns inflation. Long memory implies that shocks have a long-lasting effect. It may however be that empirical evidence for long memory is caused by neglecting one or more level shifts. Since such level shifts are not unlikely for inflation, where the shifts may be caused by sudden oil price shocks, we examine whether evidence for long memory (indicated by the relevance of an ARFIMA model) in G7 inflation rates is spurious or exaggerated. Our main findings are that apparent long memory is quite resistant to level shifts, although for a few inflation rates we find that evidence for long memory disappears.Adaptive Polar Sampling with an Application to a Bayes Measure of Value-at-Risk
http://repub.eur.nl/pub/7712/
Thu, 21 Oct 1999 00:00:01 GMT<div>L. Bauwens</div><div>C.S. Bos</div><div>H.K. van Dijk</div>
Adaptive Polar Sampling (APS) is proposed as a Markov chain Monte Carlo method for Bayesian analysis of models with ill-behaved posterior distributions. In order to sample efficiently from such a distribution, a location-scale transformation and a transformation to polar coordinates are used. After the transformation to polar coordinates, a Metropolis-Hastings algorithm is applied to sample directions and, conditionally on these, distances are generated by inverting the CDF. A sequential procedure is applied to update the location and scale.
Tested on a set of canonical models that feature near non-identifiability, strong correlation, and bimodality, APS compares favourably with the standard Metropolis-Hastings sampler in terms of parsimony and robustness. APS is applied within a Bayesian analysis of a GARCH-mixture model which is used for the evaluation of the Value-at-Risk of the return of the Dow Jones stock index.Daily exchange rate behaviour and hedging of currency risk
http://repub.eur.nl/pub/1605/
Wed, 13 Oct 1999 00:00:01 GMT<div>C.S. Bos</div><div>R.J. Mahieu</div><div>H.K. van Dijk</div>
Exchange rates typically exhibit time-varying patterns in both means and variances. The histograms of such series indicate heavy tails. In this paper we construct models which enable a decision-maker to analyze the implications of such time series patterns for currency risk management. Our approach is Bayesian where extensive use is made of Markov chain Monte Carlo methods. The effects of several model characteristics (unit roots, GARCH, stochastic volatility, heavy tailed disturbance densities) are investigated in relation to the hedging decision strategies. Consequently, we can make a distinction between statistical relevance of model specifications, and the economic consequences from a risk management point of view. The empirical results suggest that econometric modelling of heavy tails and time-varying means and variances pays off compared to a efficient markets model. The different ways to measure persistence and changing volatilities appear to strongly influence the hedging decision the investor faces.Adaptive polar sampling: a new MC technique for the analysis of ill behaved surfaces
http://repub.eur.nl/pub/1550/
Thu, 02 Jul 1998 00:00:01 GMT<div>L. Bauwens</div><div>C.S. Bos</div><div>H.K. van Dijk</div>
Adaptive Polar Sampling is proposed as an algorithm where random drawings are directly generated from the target function (posterior) in
all-but-one directions of the parameter space. The method is based on the mixed integration technique of Van Dijk, Kloek & Boender (1985) but
extends this one by replacing the one-dimensional quadrature step by Monte Carlo simulation from this one-dimensional distribution function.
The method is particularly suited for the analysis of ill-behaved surfaces. An illustrative example shows the feasibility of the
algorithm.Long memory and level shifts: re-analysing inflation rates
http://repub.eur.nl/pub/1556/
Thu, 02 Jul 1998 00:00:01 GMT<div>Ph.H.B.F. Franses</div><div>M. Ooms</div><div>C.S. Bos</div>
A key application of long memory time series models concerns inflation. Long memory implies that shocks have a long-lasting effect. It may however be that empirical evidence for long memory is caused by neglecting one or more level shifts. Since such level shifts are not unlikely for inflation, where the shifts may be caused by sudden oil price shocks, we examine whether evidence for long memory (indicated by the relevance of an ARFIMA model) in G7 inflation rates is spurious or exaggerated. Our main findings are that apparent long memory is quite resistant to level shifts, although for a few inflation rates we find that evidence for long memory disappears.Long Memory and Level Shifts: Re-Analyzing Inflation Rates
http://repub.eur.nl/pub/7759/
Fri, 27 Feb 1998 00:00:01 GMT<div>C.S. Bos</div><div>Ph.H.B.F. Franses</div><div>M. Ooms</div>
A key application of long memory time series models concerns inflation. Long memory implies that shocks have a long-lasting effect. It may however be that empirical evidence for long memory is caused by neglecting one or more level shifts. Since such level shifts are not unlikely for inflation, where the shifts may be caused by sudden oil price shocks, we examine whether evidence for long memory (indicated by the relevance of an ARFIMA model) in G7 inflation rates is spurious or exaggerated. Our main findings are that apparent long memory is quite resistant to level shifts, although for a few inflation rates we find that evidence for long memory disappears.