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Parametric Methods (parametric + methods)
Selected AbstractsStatistical models of shape for the analysis of protein spots in two-dimensional electrophoresis gel imagesPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 6 2003Mike Rogers Abstract In image analysis of two-dimensional electrophoresis gels, individual spots need to be identified and quantified. Two classes of algorithms are commonly applied to this task. Parametric methods rely on a model, making strong assumptions about spot appearance, but are often insufficiently flexible to adequately represent all spots that may be present in a gel. Nonparametric methods make no assumptions about spot appearance and consequently impose few constraints on spot detection, allowing more flexibility but reducing robustness when image data is complex. We describe a parametric representation of spot shape that is both general enough to represent unusual spots, and specific enough to introduce constraints on the interpretation of complex images. Our method uses a model of shape based on the statistics of an annotated training set. The model allows new spot shapes, belonging to the same statistical distribution as the training set, to be generated. To represent spot appearance we use the statistically derived shape convolved with a Gaussian kernel, simulating the diffusion process in spot formation. We show that the statistical model of spot appearance and shape is able to fit to image data more closely than the commonly used spot parameterizations based solely on Gaussian and diffusion models. We show that improvements in model fitting are gained without degrading the specificity of the representation. [source] System identification of instrumented bridge systemsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2003Yalin Arici Abstract Several recorded motions for seven bridge systems in California during recent earthquakes were analysed using parametric and non-parametric system identification (SI) methods. The bridges were selected considering the availability of an adequate array of accelerometers and accounting for different structural systems, materials, geometry and soil types. The results of the application of SI methods included identification of modal frequencies and damping ratios. Excellent fits of the recorded motion in the time domain were obtained using parametric methods. The multi-input/single-output SI method was a suitable approach considering the instrumentation layout for these bridges. Use of the constructed linear filters for prediction purposes was also demonstrated for three bridge systems. Reasonable prediction results were obtained considering the various limitations of the procedure. Finally, the study was concluded by identifying the change of the modal frequencies and damping of a particular bridge system in time using recursive filters. Copyright © 2003 John Wiley & Sons, Ltd. [source] Estimating the Impact of a Policy Reform on Benefit Take-up: The 2001 extension to the Minimum Income Guarantee for UK PensionersECONOMICA, Issue 306 2010FRANCESCA ZANTOMIO In 2001 the Minimum Income Guarantee for UK pensioners was reformed, changing the structure and level of benefits. We evaluate the behavioural response to this reform, using nonparametric analysis comparing a sample of pensioners interviewed before and another interviewed after the reform, matching their simulated pre- and post-reform entitlements and other characteristics. We compare the results with conventional parametric methods and also ex ante matching, and we consider the effect of measurement error in simulated entitlements. The response of take-up to the reform is found to be significant and positive, with evidence of larger impacts from the nonparametric analysis. [source] The Wealth Effect on New Business Startups in a Developing EconomyECONOMICA, Issue 291 2006ALICE MESNARD The paper tests for nonlinearities in the wealth effect on self-employment, as can arise from startup costs or liquidity constraints. Using both nonparametric and parametric methods, we show that the relationship between the probability of a return migrant to Tunisia starting up a business and the stock of his savings repatriated at return is concave for almost the entire range of our data, though we find weak evidence of a convex relationship at very low wealth levels. Our results suggest that the aggregate self-employment rate is an increasing function of aggregate wealth, but a decreasing function of wealth inequality. [source] An improvement of quantum parametric methods by using SGSA parameterization technique and new elementary parametric functionalsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3 2010M. Sánchez Abstract A systematic improvement of parametric quantum methods (PQM) is performed by considering: (a) a new application of parameterization procedure to PQMs and (b) novel parametric functionals based on properties of elementary parametric functionals (EPF) [Ruette et al., Int J Quantum Chem 2008, 108, 1831]. Parameterization was carried out by using the simplified generalized simulated annealing (SGSA) method in the CATIVIC program. This code has been parallelized and comparison with MOPAC/2007 (PM6) and MINDO/SR was performed for a set of molecules with CC, CH, and HH bonds. Results showed better accuracy than MINDO/SR and MOPAC-2007 for a selected trial set of molecules. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Parametric and semiparametric estimation of sample selection models: an empirical application to the female labour force in PortugalJOURNAL OF APPLIED ECONOMETRICS, Issue 1 2001Maria Fraga O. Martins This paper applies both parametric and semiparametric methods to the estimation of wage and participation equations for married women in Portugal. The semiparametric estimators considered are the two-stage estimators proposed by Newey (1991) and Andrews and Schafgans (1998). The selection equation results are compared using the specification tests proposed by Horowitz (1993), Horowitz and Härdle (1994), and the wage equation results are compared using a Hausman test. Significant differences between the two approaches indicate the inappropriateness of the standard parametric methods to the estimation of the model and for the purpose of policy simulations. The greater departure seems to occur in the range of the low values of the index corresponding to a specific group of women. Copyright © 2001 John Wiley & Sons, Ltd. [source] Non-parametric permutation test for the discrimination of float glass samples based on LIBS spectraJOURNAL OF CHEMOMETRICS, Issue 6 2010Erin McIntee Abstract Laser-induced breakdown spectroscopy (LIBS) coupled with non-parametric permutation based hypothesis testing is demonstrated to have good performance in discriminating float glass samples. This type of pairwise sample comparison is important in manufacturing process quality control, forensic science and other applications where determination of a match probability between two samples is required. Analysis of the pairwise comparisons between multiple LIBS spectra from a single glass sample shows that some assumptions required by parametric methods may not hold in practice, motivating the adoption of a non-parametric permutation test. Without rigid distributional assumptions, the permutation test exhibits excellent discriminating power while holding the actual size of Type I error at the nominal level. Copyright © 2010 John Wiley & Sons, Ltd. [source] MMPI-2 profiles of Gulf and Vietnam combat veterans with chronic posttraumatic stress disorderJOURNAL OF CLINICAL PSYCHOLOGY, Issue 4 2002D. Michael Glenn The current study examined service era differences in a sample of 172 Gulf and Vietnam outpatient veterans with combat-related posttraumatic stress disorder (PTSD). Participants completed the MMPI-2 and several additional self-report measures of symptom severity (PTSD, depression, anxiety, hostility, and health complaints). Results indicated that MMPI-2 profiles differed significantly according to service era with Vietnam veterans scoring higher on scales 2, 8, and 0 and lower on scale 9 than did Gulf veterans. Examination of group means derived from parametric analysis of MMPI-2 data suggested a mean two-point code type of 2,8/8,2 for Vietnam veterans and 1,8/8,1 for Gulf veterans. In contrast, when the data were examined using descriptive techniques based on frequency counts of individual MMPI-2 profiles, the most frequently occurring two-point codetype was 7,8/8,7 for Vietnam veterans, and 6,8/8,6 for Gulf veterans. In addition, Gulf veterans reported a greater number of total health complaints than Vietnam veterans, whereas Vietnam veterans reported a greater number of physician-diagnosed physical conditions. Potential advantages of incorporating descriptive approaches versus parametric methods when examining profile data are also presented. © 2002 Wiley Periodicals, Inc. J Clin Psychol 58: 371,381, 2002. [source] Toward accurate relative energy predictions of the bioactive conformation of drugsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 4 2009Keith T. Butler Abstract Quantifying the relative energy of a ligand in its target-bound state (i.e. the bioactive conformation) is essential to understand the process of molecular recognition, to optimize the potency of bioactive molecules and to increase the accuracy of structure-based drug design methods. This is, nevertheless, seriously hampered by two interrelated issues, namely the difficulty in carrying out an exhaustive sampling of the conformational space and the shortcomings of the energy functions, usually based on parametric methods of limited accuracy. Matters are further complicated by the experimental uncertainty on the atomic coordinates, which precludes a univocal definition of the bioactive conformation. In this article we investigate the relative energy of bioactive conformations introducing two major improvements over previous studies: the use sophisticated QM-based methods to take into account both the internal energy of the ligand and the solvation effect, and the application of physically meaningful constraints to refine the bioactive conformation. On a set of 99 drug-like molecules, we find that, contrary to previous observations, two thirds of bioactive conformations lie within 0.5 kcal mol,1 of a local minimum, with penalties above 2.0kcal mol,1 being generally attributable to structural determination inaccuracies. The methodology herein described opens the door to obtain quantitative estimates of the energy of bioactive conformations and can be used both as an aid in refining crystallographic structures and as a tool in drug discovery. © 2008 Wiley Periodicals, Inc. J Comput Chem 2009 [source] Selection of evolutionary models for phylogenetic hypothesis testing using parametric methodsJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2001B. C. Emerson Recent molecular studies have incorporated the parametric bootstrap method to test a priori hypotheses when the results of molecular based phylogenies are in conflict with these hypotheses. The parametric bootstrap requires the specification of a particular substitutional model, the parameters of which will be used to generate simulated, replicate DNA sequence data sets. It has been both suggested that, (a) the method appears robust to changes in the model of evolution, and alternatively that, (b) as realistic model of DNA substitution as possible should be used to avoid false rejection of a null hypothesis. Here we empirically evaluate the effect of suboptimal substitution models when testing hypotheses of monophyly with the parametric bootstrap using data sets of mtDNA cytochrome oxidase I and II (COI and COII) sequences for Macaronesian Calathus beetles, and mitochondrial 16S rDNA and nuclear ITS2 sequences for European Timarcha beetles. Whether a particular hypothesis of monophyly is rejected or accepted appears to be highly dependent on whether the nucleotide substitution model being used is optimal. It appears that a parameter rich model is either equally or less likely to reject a hypothesis of monophyly where the optimal model is unknown. A comparison of the performance of the Kishino,Hasegawa (KH) test shows it is not as severely affected by the use of suboptimal models, and overall it appears to be a less conservative method with a higher rate of failure to reject null hypotheses. [source] Asymptotic self-similarity and wavelet estimation for long-range dependent fractional autoregressive integrated moving average time series with stable innovationsJOURNAL OF TIME SERIES ANALYSIS, Issue 2 2005Stilian Stoev Primary 60G18; 60E07; Secondary 62M10; 63G20 Abstract., Methods for parameter estimation in the presence of long-range dependence and heavy tails are scarce. Fractional autoregressive integrated moving average (FARIMA) time series for positive values of the fractional differencing exponent d can be used to model long-range dependence in the case of heavy-tailed distributions. In this paper, we focus on the estimation of the Hurst parameter H = d + 1/, for long-range dependent FARIMA time series with symmetric , -stable (1 < , < 2) innovations. We establish the consistency and the asymptotic normality of two types of wavelet estimators of the parameter H. We do so by exploiting the fact that the integrated series is asymptotically self-similar with parameter H. When the parameter , is known, we also obtain consistent and asymptotically normal estimators for the fractional differencing exponent d = H , 1/,. Our results hold for a larger class of causal linear processes with stable symmetric innovations. As the wavelet-based estimation method used here is semi-parametric, it allows for a more robust treatment of long-range dependent data than parametric methods. [source] Analyzing Roll Calls with Perfect Spatial Voting: France 1946,1958AMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 3 2004Howard Rosenthal A recent methodological advance in legislative roll-call analysis is especially relevant to the study of legislative behavior outside the setting of the United States Congress. We argue that Poole's (2000) optimal classification method for roll-call analysis is preferable to parametric methods for studying many legislatures. This is because the nature of party discipline, near-perfect spatial voting, and parliamentary institutions that provides incentives for strategic behavior lead to severe violations of the error assumptions underlying parametric methods. The robustness of the nonparametric method to the stochastic nature of the data makes it an ideal candidate for studying strategic behavior in legislatures. We illustrate these points with an analysis of data from the French Fourth Republic (1946,1958). [source] Persistence in some energy futures marketsTHE JOURNAL OF FUTURES MARKETS, Issue 5 2010Juncal Cunado In this study, we examine the possibility of long-range dependence in some energy futures markets for different maturities. In order to test for persistence, we use a variety of techniques based on non-parametric, semi-parametric and parametric methods. The results indicate that there is little or no evidence of long memory in gasoline, propane, oil and heating oil at different maturities. However, when we focus on the volatility process, proxied by the absolute returns, we find strong evidence of long memory in all the variables at different contracts. © 2009 Wiley Periodicals, Inc. Jrl Fut Mark 30:490,507, 2010 [source] Some contributions to the analysis of multivariate dataBIOMETRICAL JOURNAL, Issue 2 2009Arne C. Bathke Abstract In this paper, we provide an overview of recently developed methods for the analysis of multivariate data that do not necessarily emanate from a normal universe. Multivariate data occur naturally in the life sciences and in other research fields. When drawing inference, it is generally recommended to take the multivariate nature of the data into account, and not merely analyze each variable separately. Furthermore, it is often of major interest to select an appropriate set of important variables. We present contributions in three different, but closely related, research areas: first, a general approach to the comparison of mean vectors, which allows for profile analysis and tests of dimensionality; second, non-parametric and parametric methods for the comparison of independent samples of multivariate observations; and third, methods for the situation where the experimental units are observed repeatedly, for example, over time, and the main focus is on analyzing different time profiles when the number p of repeated observations per subject is larger than the number n of subjects. [source] Youden Index and Optimal Cut-Point Estimated from Observations Affected by a Lower Limit of DetectionBIOMETRICAL JOURNAL, Issue 3 2008Marcus D. Ruopp Abstract The receiver operating characteristic (ROC) curve is used to evaluate a biomarker's ability for classifying disease status. The Youden Index (J), the maximum potential effectiveness of a biomarker, is a common summary measure of the ROC curve. In biomarker development, levels may be unquantifiable below a limit of detection (LOD) and missing from the overall dataset. Disregarding these observations may negatively bias the ROC curve and thus J. Several correction methods have been suggested for mean estimation and testing; however, little has been written about the ROC curve or its summary measures. We adapt non-parametric (empirical) and semi-parametric (ROC-GLM [generalized linear model]) methods and propose parametric methods (maximum likelihood (ML)) to estimate J and the optimal cut-point (c *) for a biomarker affected by a LOD. We develop unbiased estimators of J and c * via ML for normally and gamma distributed biomarkers. Alpha level confidence intervals are proposed using delta and bootstrap methods for the ML, semi-parametric, and non-parametric approaches respectively. Simulation studies are conducted over a range of distributional scenarios and sample sizes evaluating estimators' bias, root-mean square error, and coverage probability; the average bias was less than one percent for ML and GLM methods across scenarios and decreases with increased sample size. An example using polychlorinated biphenyl levels to classify women with and without endometriosis illustrates the potential benefits of these methods. We address the limitations and usefulness of each method in order to give researchers guidance in constructing appropriate estimates of biomarkers' true discriminating capabilities. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||