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Selected AbstractsFish-based methods for assessing European running waters: a synthesisFISHERIES MANAGEMENT & ECOLOGY, Issue 6 2007S. SCHMUTZ Abstract, The European Union, Water Framework Directive (WFD) requires monitoring of riverine fish fauna. When the WFD came into force in 2000, most of the EU member states did not have fish-based assessment methods compliant to WFD requirements. Therefore, the objectives of FAME (http://fame.boku.ac.at), a project under the fifth R&D Framework Programme of the European Commission were to develop, evaluate and implement a standardised fish-based method for assessing the ecological status of European running waters. This paper synthesises the outputs of FAME and defines future research needs. Two different methodologies were used: the so-called spatially based modelling and the site-specific modelling, the latter leading to the European Fish Index (EFI). The advantage of the EFI is that, despite being a single index, it is applicable to a wide range of environmental conditions across Europe precluding the need for inter-calibration. The EFI will support the WFD towards harmonised/standardised assessment and management of running waters in Europe, thus enabling comparative analyses of the ecological status of running waters across Europe. [source] Measuring and partitioning the high-order linkage disequilibrium by multiple order Markov chainsGENETIC EPIDEMIOLOGY, Issue 4 2008Yunjung Kim Abstract A map of the background levels of disequilibrium between nearby markers can be useful for association mapping studies. In order to assess the background levels of linkage disequilibrium (LD), multilocus LD measures are more advantageous than pairwise LD measures because the combined analysis of pairwise LD measures is not adequate to detect simultaneous allele associations among multiple markers. Various multilocus LD measures based on haplotypes have been proposed. However, most of these measures provide a single index of association among multiple markers and does not reveal the complex patterns and different levels of LD structure. In this paper, we employ non-homogeneous, multiple order Markov Chain models as a statistical framework to measure and partition the LD among multiple markers into components due to different orders of marker associations. Using a sliding window of multiple markers on phased haplotype data, we compute corresponding likelihoods for different Markov Chain (MC) orders in each window. The log-likelihood difference between the lowest MC order model (MC0) and the highest MC order model in each window is used as a measure of the total LD or the overall deviation from the gametic equilibrium for the window. Then, we partition the total LD into lower order disequilibria and estimate the effects from two-, three-, and higher order disequilibria. The relationship between different orders of LD and the log-likelihood difference involving two different orders of MC models are explored. By applying our method to the phased haplotype data in the ENCODE regions of the HapMap project, we are able to identify high/low multilocus LD regions. Our results reveal that the most LD in the HapMap data is attributed to the LD between adjacent pairs of markers across the whole region. LD between adjacent pairs of markers appears to be more significant in high multilocus LD regions than in low multilocus LD regions. We also find that as the multilocus total LD increases, the effects of high-order LD tends to get weaker due to the lack of observed multilocus haplotypes. The overall estimates of first, second, third, and fourth order LD across the ENCODE regions are 64, 23, 9, and 3%. Genet. Epidemiol. 2008. © 2008 Wiley-Liss, Inc. [source] Using DCE and ranking data to estimate cardinal values for health states for deriving a preference-based single index from the sexual quality of life questionnaireHEALTH ECONOMICS, Issue 11 2009Julie Ratcliffe Abstract There is an increasing interest in using data derived from ordinal methods, particularly data derived from discrete choice experiments (DCEs), to estimate the cardinal values for health states to calculate quality adjusted life years (QALYs). Ordinal measurement strategies such as DCE may have considerable practical advantages over more conventional cardinal measurement techniques, e.g. time trade-off (TTO), because they may not require such a high degree of abstract reasoning. However, there are a number of challenges to deriving the cardinal values for health states using ordinal data, including anchoring the values on the full health,dead scale used to calculate QALYs. This paper reports on a study that deals with these problems in the context of using two ordinal techniques, DCE and ranking, to derive the cardinal values for health states derived from a condition-specific sexual health measure. The results were compared with values generated using a commonly used cardinal valuation technique, the TTO. This study raises some important issues about the use of ordinal data to produce cardinal health state valuations. Copyright © 2009 John Wiley & Sons, Ltd. [source] A critique of the World Health Organisation's evaluation of health system performanceHEALTH ECONOMICS, Issue 5 2003Jeff Richardson Abstract The World Health Organisation's (WHO) approach to the measurement of health system efficiency is briefly described. Four arguments are then presented. First, equity of finance should not be a criterion for the evaluation of a health system and, more generally, the same objectives and importance weights should not be imposed upon all countries. Secondly, the numerical value of the importance weights do not reflect their true importance in the country rankings. Thirdly, the model for combining the different objectives into a single index of system performance is problematical and alternative models are shown to alter system rankings. The WHO statistical analysis is replicated and used to support the fourth argument which is that, contrary to the author's assertion, their methods cannot separate true inefficiency from random error. The procedure is also subject to omitted variable bias. The econometric model for all countries has very poor predictive power for the subset of OECD countries and it is outperformed by two simpler algorithms. Country rankings based upon the model are correspondingly unreliable. It is concluded that, despite these problems, the study is a landmark in the evolution of system evaluation, but one which requires significant revision. Copyright © 2002 John Wiley & Sons, Ltd. [source] Study of indices for drought characterization in KBK districts in Orissa (India)HYDROLOGICAL PROCESSES, Issue 12 2008R. P. Pandey Abstract Drought is a temporary, random and regional climatic phenomenon, originating due to lack of precipitation leading to water deficit and causing economic loss. Success in drought alleviation depends on how well droughts are defined and their severity quantified. A quantitative definition identifies the beginning, end, spatial extent and the severity of drought. Among the available indices, no single index is capable of fully describing all the physical characteristics of drought. Therefore, in most cases it is useful and necessary to consider several indices, examine their sensitivity and accuracy, and investigate for correlation among them. In this study, the geographical information system-based Spatial and Time Series Information Modeling (SPATSIM) and Daily Water Resources Assessment Modeling (DWRAM) software were used for drought analysis on monthly and daily bases respectively and its spatial distribution in both dry and wet years. SPATSIM utilizes standardized precipitation index (SPI), effective drought index (EDI), deciles index and departure from long-term mean and median; and DWRAM employs only EDI. The analysis of data from the Kalahandi and Nuapada districts of Orissa (India) revealed that (a) droughts in this region occurred with a frequency of once in every 3 to 4 years, (b) droughts occurred in the year when the ratio of annual rainfall to potential evapotranspiration (Pae/PET) was less than 0·6, (c) EDI better represented the droughts in the area than any other index; (d) all SPI, EDI and annual deviation from the mean showed a similar trend of drought severity. The comparison of all indices and results of analysis led to several useful and pragmatic inferences in understanding the drought attributes of the study area. Copyright © 2007 John Wiley & Sons, Ltd. [source] THE TEN COMMANDMENTS FOR OPTIMIZING VALUE-AT-RISK AND DAILY CAPITAL CHARGESJOURNAL OF ECONOMIC SURVEYS, Issue 5 2009Michael McAleer Abstract Credit risk is the most important type of risk in terms of monetary value. Another key risk measure is market risk, which is concerned with stocks and bonds, and related financial derivatives, as well as exchange rates and interest rates. This paper is concerned with market risk management and monitoring under the Basel II Accord, and presents Ten Commandments for optimizing value-at-risk (VaR) and daily capital charges, based on choosing wisely from (1) conditional, stochastic and realized volatility; (2) symmetry, asymmetry and leverage; (3) dynamic correlations and dynamic covariances; (4) single index and portfolio models; (5) parametric, semi-parametric and non-parametric models; (6) estimation, simulation and calibration of parameters; (7) assumptions, regularity conditions and statistical properties; (8) accuracy in calculating moments and forecasts; (9) optimizing threshold violations and economic benefits; and (10) optimizing private and public benefits of risk management. For practical purposes, it is found that the Basel II Accord would seem to encourage excessive risk taking at the expense of providing accurate measures and forecasts of risk and VaR. [source] Identification and estimation of local average derivatives in non-separable models without monotonicityTHE ECONOMETRICS JOURNAL, Issue 1 2009Stefan Hoderlein Summary, In many structural economic models there are no good arguments for additive separability of the error. Recently, this motivated intensive research on non-separable structures. For instance, in Hoderlein and Mammen (2007) a non-separable model in the single equation case was considered, and it was established that in the absence of the frequently employed monotonicity assumption local average structural derivatives (LASD) are still identified. In this paper, we introduce an estimator for the LASD. The estimator we propose is based on local polynomial fitting of conditional quantiles. We derive its large sample distribution through a Bahadur representation, and give some related results, e.g. about the asymptotic behaviour of the quantile process. Moreover, we generalize the concept of LASD to include endogeneity of regressors and discuss the case of a multivariate dependent variable. We also consider identification of structured non-separable models, including single index and additive models. We discuss specification testing, as well as testing for endogeneity and for the impact of unobserved heterogeneity. We also show that fixed censoring can easily be addressed in this framework. Finally, we apply some of the concepts to demand analysis using British Consumer Data. [source] Asymmetric hedging of the corporate terms of tradeTHE JOURNAL OF FUTURES MARKETS, Issue 11 2006Roger Bowden Risk management techniques such as value at risk and conditional value at risk focus attention on protecting the downside exposures without penalizing the upside exposures. The implied welfare functions are equivalent to an otherwise risk neutral agent with a put option exposure on the downside. The correspondence can be exploited to design smoother loss measures and numerically based solutions for optimal hedge ratios. A statistically well-adapted hedge object for the firm is the corporate terms of trade, which balances up output and expense prices as a single index related to the net profit margin. The methods are applied to the NZ dairy industry to derive optimal foreign exchange forwards based hedges. It is not always optimal to rely solely on forward discounts or premiums. © 2006 Wiley Periodicals, Inc. Jrl Fut Mark 26:1059,1088, 2006 [source] Measurement of Outcome: A Proposed SchemeTHE MILBANK QUARTERLY, Issue 4 2005BARBARA STARFIELD The need to demonstrate that health care has an influence on health status is increasingly pressing. Such demonstrations require tools of measurement which are unfortunately not available. Development of instruments has been hampered by a lack of consensus on appropriate frames of reference, and there appears to be little agreement on what should be measured and what relative importance should be ascribed to different dimensions of health status. An approach that does not require the assignment of numerical values or weights to various aspects of health status and is applicable to all age groups within the population and to the whole spectrum of health problems rather than to specific medical diagnoses would seem desirable. A scheme that is based upon the development of a "profile" rather than a single "index" for describing health status is proposed in this paper. The model is a conceptual framework whose usefulness will depend upon efforts of a large number of researchers from many disciplines to develop instruments which can be incorporated in it. Although the problems in development of the scheme are complex, I hope that it will focus attention on the relevant dimensions and facilitate improved coordination of efforts to produce ways to demonstrate what health care contributes to health. [source] Area under the Free-Response ROC Curve (FROC) and a Related Summary IndexBIOMETRICS, Issue 1 2009Andriy I. Bandos Summary Free-response assessment of diagnostic systems continues to gain acceptance in areas related to the detection, localization, and classification of one or more "abnormalities" within a subject. A free-response receiver operating characteristic (FROC) curve is a tool for characterizing the performance of a free-response system at all decision thresholds simultaneously. Although the importance of a single index summarizing the entire curve over all decision thresholds is well recognized in ROC analysis (e.g., area under the ROC curve), currently there is no widely accepted summary of a system being evaluated under the FROC paradigm. In this article, we propose a new index of the free-response performance at all decision thresholds simultaneously, and develop a nonparametric method for its analysis. Algebraically, the proposed summary index is the area under the empirical FROC curve penalized for the number of erroneous marks, rewarded for the fraction of detected abnormalities, and adjusted for the effect of the target size (or "acceptance radius"). Geometrically, the proposed index can be interpreted as a measure of average performance superiority over an artificial "guessing" free-response process and it represents an analogy to the area between the ROC curve and the "guessing" or diagonal line. We derive the ideal bootstrap estimator of the variance, which can be used for a resampling-free construction of asymptotic bootstrap confidence intervals and for sample size estimation using standard expressions. The proposed procedure is free from any parametric assumptions and does not require an assumption of independence of observations within a subject. We provide an example with a dataset sampled from a diagnostic imaging study and conduct simulations that demonstrate the appropriateness of the developed procedure for the considered sample sizes and ranges of parameters. [source] Time-Varying Functional Regression for Predicting Remaining Lifetime Distributions from Longitudinal TrajectoriesBIOMETRICS, Issue 4 2005Hans-Georg Müller Summary A recurring objective in longitudinal studies on aging and longevity has been the investigation of the relationship between age-at-death and current values of a longitudinal covariate trajectory that quantifies reproductive or other behavioral activity. We propose a novel technique for predicting age-at-death distributions for situations where an entire covariate history is included in the predictor. The predictor trajectories up to current time are represented by time-varying functional principal component scores, which are continuously updated as time progresses and are considered to be time-varying predictor variables that are entered into a class of time-varying functional regression models that we propose. We demonstrate for biodemographic data how these methods can be applied to obtain predictions for age-at-death and estimates of remaining lifetime distributions, including estimates of quantiles and of prediction intervals for remaining lifetime. Estimates and predictions are obtained for individual subjects, based on their observed behavioral trajectories, and include a dimension-reduction step that is implemented by projecting on a single index. The proposed techniques are illustrated with data on longitudinal daily egg-laying for female medflies, predicting remaining lifetime and age-at-death distributions from individual event histories observed up to current time. [source] | |||||||||||||