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Bootstrap Simulations (bootstrap + simulation)
Selected AbstractsCharacterization and uncertainty analysis of VOCs emissions from industrial wastewater treatment plantsENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2010Kaishan Zhang Abstract Air toxics from the industrial wastewater treatment plants (IWTPs) impose serious health concerns on its surrounding residential neighborhoods. To address such health concerns, one of the key challenges is to quantify the air emissions from the IWTPs. The objective here is to characterize the air emissions from the IWTPs and quantify its associated uncertainty. An IWTP receiving the wastewaters from an airplane maintenance facility is used for illustration with focus on the quantification of air emissions for benzyl alcohol, phenol, methylene chloride, 2-butanone, and acetone. Two general fate models, i.e., WATER9 and TOXCHEM+V3.0 were used to model the IWTP and quantify the air emissions. Monte Carlo and Bootstrap simulation were used for uncertainty analysis. On average, air emissions from the IWTP were estimated to range from 0.003 lb/d to approximately 16 lb/d with phenol being the highest and benzyl alcohol being the least. However, emissions are associated with large uncertainty. The ratio of the 97.5th percentile to the 2.5th percentile air emissions ranged from 5 to 50 depending on pollutants. This indicates point estimates of air emissions might fail to capture the worst scenarios, leading to inaccurate conclusion when used for health risk assessment. © 2009 American Institute of Chemical Engineers Environ Prog, 2010 [source] Bootstrap simulations for evaluating the uncertainty associated with peaks-over-threshold estimates of extreme wind velocityENVIRONMETRICS, Issue 1 2003M. D. Pandey Abstract In the peaks-over-threshold (POT) method of extreme quantile estimation, the selection of a suitable threshold is critical to estimation accuracy. In practical applications, however, the threshold selection is not so obvious due to erratic variation of quantile estimates with minor changes in threshold. To address this issue, the article investigates the variation of quantile uncertainty (bias and variance) as a function of threshold using a semi-parametric bootstrap algorithm. Furthermore, the article compares the performance of L-moment and de Haan methods that are used for fitting the Pareto distribution to peak data. The analysis of simulated and actual U.S. wind speed data illustrates that the L-moment method can lead to almost unbiased quantile estimates for certain thresholds. A threshold corresponding to minimum standard error appears to provide reasonable estimates of wind speed extremes. It is concluded that the quantification of uncertainty associated with a quantile estimate is necessary for selecting a suitable threshold and estimating the design wind speed. For this purpose, semi-parametric bootstrap method has proved to be a simple, practical and effective tool. Copyright © 2003 John Wiley & Sons, Ltd. [source] Simple Trading Rules and the Market for Internet StocksINTERNATIONAL REVIEW OF FINANCE, Issue 4 2001Wai Mun Fong We investigate the profitability of moving average trading rules for Internet stocks based on the Dow Jones Internet Composite Index. Consistent with previous studies e.g. Brock et al. (1992), returns after buy signals exceed returns after sell signals. The average buy,sell spread is large and significant even after accounting for transaction costs. Bootstrap simulations based on a version of the dynamic CAPM show that the model is able to replicate the pattern of buy and sell returns. Simulated buy,sell spreads amount on average to more than 39% of the actual spread. However, actual profits are still too large to be explained in terms of risk compensation. [source] Luck versus Skill in the Cross-Section of Mutual Fund ReturnsTHE JOURNAL OF FINANCE, Issue 5 2010EUGENE F. FAMA ABSTRACT The aggregate portfolio of actively managed U.S. equity mutual funds is close to the market portfolio, but the high costs of active management show up intact as lower returns to investors. Bootstrap simulations suggest that few funds produce benchmark-adjusted expected returns sufficient to cover their costs. If we add back the costs in fund expense ratios, there is evidence of inferior and superior performance (nonzero true ,) in the extreme tails of the cross-section of mutual fund , estimates. [source] Glucosamine sulphate in the treatment of knee osteoarthritis: cost-effectiveness comparison with paracetamolINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 6 2010S. Scholtissen Summary Introduction:, The aim of this study was to explore the cost-effectiveness of glucosamine sulphate (GS) compared with paracetamol and placebo (PBO) in the treatment of knee osteoarthritis. For this purpose, a 6-month time horizon and a health care perspective was used. Material and methods:, The cost and effectiveness data were derived from Western Ontario and McMaster Universities Osteoarthritis Index data of the Glucosamine Unum In Die (once-a-day) Efficacy trial study by Herrero-Beaumont et al. Clinical effectiveness was converted into utility scores to allow for the computation of cost per quality-adjusted life year (QALY) For the three treatment arms Incremental Cost-Effectiveness Ratio were calculated and statistical uncertainty was explored using a bootstrap simulation. Results:, In terms of mean utility score at baseline, 3 and 6 months, no statistically significant difference was observed between the three groups. When considering the mean utility score changes from baseline to 3 and 6 months, no difference was observed in the first case but there was a statistically significant difference from baseline to 6 months with a p-value of 0.047. When comparing GS with paracetamol, the mean baseline incremental cost-effectiveness ratio (ICER) was dominant and the mean ICER after bootstrapping was ,1376 ,/QALY indicating dominance (with 79% probability). When comparing GS with PBO, the mean baseline and after bootstrapping ICER were 3617.47 and 4285 ,/QALY, respectively. Conclusion:, The results of the present cost-effectiveness analysis suggested that GS is a highly cost-effective therapy alternative compared with paracetamol and PBO to treat patients diagnosed with primary knee OA. [source] Importance of assemblage-level thinning: A field experiment in an alpine meadow on the Tibet plateauJOURNAL OF VEGETATION SCIENCE, Issue 4 2006Yanjiang Luo Anon. (1998) Abstract Question: Which fraction of the decrease in species richness under fertilization can be explained by assemblage-level thinning? Location: An alpine meadow on the eastern Tibet plateau. Methods: 60-m2 plots were randomly assigned to a control or one of four levels of ammonium phosphate fertilizer. Treatments were repeated for three years. The effect of as semblage-level thinning was decided based on similarity in quadrats within and between fertilizing levels, bootstrap simulation based on random thinning of the high density (low production, low fertility) quadrats and correlation of species' biomass in low fertility and high fertility. Results: Fertilization increased production, reduced species richness and reduced density of individuals. Heavily fertilized quadrats are more similar in species composition in 2000 but less similar in 2001 and 2002. Rarefaction showed that a decrease in density can account for 32.3-42.9% decrease of species richness, but the simulated species richness is always significantly higher than the observed one. When production and species richness are similar at two levels of fertilization, species biomass in the higher fertility treatment is positively correlated with biomass at lower fertility. When the two fertilizer levels differed in production and species richness, there was no evidence of correlation in species biomass, suggesting that assemblage level thinning cannot explain all the loss of species. Conclusion: Although a decrease in density could explain much of the decrease (up to 42.9%) in species richness when this alpine meadow was fertilized, other important mechanisms such as interspecific competition cannot be ignored. Future studies should investigate the effect of assemblage level thinning on species diversity, and search for mechanisms responsible for a decrease in diversity. [source] A Three-step Method for Choosing the Number of Bootstrap RepetitionsECONOMETRICA, Issue 1 2000Donald W. K. Andrews This paper considers the problem of choosing the number of bootstrap repetitions B for bootstrap standard errors, confidence intervals, confidence regions, hypothesis tests, p -values, and bias correction. For each of these problems, the paper provides a three-step method for choosing B to achieve a desired level of accuracy. Accuracy is measured by the percentage deviation of the bootstrap standard error estimate, confidence interval length, test's critical value, test's p -value, or bias-corrected estimate based on B bootstrap simulations from the corresponding ideal bootstrap quantities for which B=,. The results apply quite generally to parametric, semiparametric, and nonparametric models with independent and dependent data. The results apply to the standard nonparametric iid bootstrap, moving block bootstraps for time series data, parametric and semiparametric bootstraps, and bootstraps for regression models based on bootstrapping residuals. Monte Carlo simulations show that the proposed methods work very well. [source] Purchasing Power Parity Adjustment Speeds in High Frequency Data when the Equilibrium Real Exchange Rate is Proxied by a Deterministic TrendTHE MANCHESTER SCHOOL, Issue 2003Ivan Paya Rogoff suggested in 1996 that the dollar,yen real exchange rate represented a ,canonical' case of a trend in the equilibrium real exchange rate. The implied speed of adjustment of the dollar,yen real exchange rate is found to be substantially faster, with half-life shocks of less than 2 years, from estimates of a non-linear model which incorporates a deterministic trend proxying the equilibrium level. We also examine the power of unit root tests against smooth transition non-linear models which incorporate a deterministic trend and the robustness of such non-linear estimations using Monte Carlo and bootstrap simulations. [source] | ||||||||||