Selection Of Estimation Method Research Articles

Simultaneous variable selection and estimation for multivariate multilevel longitudinal data with both continuous and binary responses

Complex structured data settings are studied where outcomes are multivariate and multilevel and are collected longitudinally. Multivariate outcomes include both continuous and discrete responses. In addition, the data contain a large number of covariates but only some of them are important in explaining the dynamic features of the responses. To delineate the complex association structures of the responses, a model with correlated random effects is proposed. To handle the large dimensionality of covariates, a simultaneous variable selection and parameter estimation method is developed. To implement the method, a computationally feasible algorithm is described. The proposed method is evaluated empirically by simulation studies and illustrated by analyzing the data arising from the Waterloo Smoking Prevention Project.

Optimized activity ratio for different types of reagent attachment at sulfide minerals

The authors evaluate the ratio of activities exhibited by physical and chemical adsorptions of an agent on sulfide minerals. The following assumptions are made: 1) the main kinetic restriction for flotation contact (particle–bubble interaction) is the film between mineral particle and air bubble; 2) water is removed from the film by both physical and chemical adsorptions; 3) the water volume removed by physical adsorption is conditioned by the difference in the volumes of water in the films bounded by meniscuses with advancing angle ΘA and receding angle ΘR and neck radius R. The water volume removed under the action of surface forces (hydrophobic, dispersive) was disregarded as the agent attachment was low dense and mosaic. The article reports experimental data on limit values of static advancing and receding angles on the surface of some sulfide metals. It is shown that selectivity of flotation of sulfides depends on the ratio of water volumes removed from the film by desorbable physical adsorption and non-desorbable chemical adsorption types of agents. The proposed method of selectivity estimation is suitable for minerals with similar (close) properties of the surface when stabilizing ion–electrostatic interaction between minerals and air bubbles is absent or insignificant. The calculation results may be of use to optimizing collecting ability of physically adsorbed low-polar or desorbable species of ionized agent with intent to improve selectivity of separation of sulfide minerals.

An accurate selectivity estimation method for window queries and an implementation thereof

Spatial selectivity estimation is crucial to choose the cheapest execution plan for a given query in a query optimizer. This article proposes an accurate spatial selectivity estimation method based on the cumulative density (CD) histograms, which can deal with any arbitrary spatial query window. In this method, the selectivity can be estimated in original logic of the CD histogram, after the four corner values of a query window have been accurately interpolated on the continuous surface of the elevation histogram. For the interpolation of any corner points, we first identify the cells that can affect the value of point (x, y) in the CD histogram. These cells can be categorized into two classes: ones within the range from (0, 0) to (x, y) and the other overlapping the range from (0, 0) to (x, y). The values of the former class can be used directly, whereas we revise the values of any cells falling in the latter class by the number of vertices in the corresponding cell and the area ratio covered by the range from (0, 0) to (x, y). This revision makes the estimation method more accurate. The CD histograms and estimation method have been implemented in INGRES. Experiment results show that the method can accurately estimate the selectivity of arbitrary query windows and can help the optimizer choose a cheaper query plan.

Comparison of Estimators of Gumbel Distribution for Assessment of Seasonal and Annual Rainfall

Estimation of seasonal and annual rainfall for a river basin is of importance in planning and management of water resources projects. This study illustrates the use of six different parameter estimation methods for Gumbel distribution for assessment of seasonal and annual rainfall for Krishna and Godavari river basins. Goodness-of-Fit tests involving Anderson–Darling and Kolmogorov–Smirnov are used for checking the adequacy of fitting of Gumbel distribution to the recorded rainfall data. Model performance indicators such as correlation coefficient, model efficiency and root mean square error are used for the selection of suitable method for estimation of rainfall. The study shows that the probability weighted moments are better suited for determination of parameters of Gumbel distribution for assessment of seasonal and annual rainfall for Krishna and Godavari basins.

Validated Stability Indicating RP-HPLC Method for Simultaneous Estimation of Ofloxacin and Cefixime in their Combined Dosage Form

The objective of the current study was to develop and validate a simple, accurate, precise and selective stability-indicating gradient reverse phase high performance liquid chromatographic method for simultaneous estimation of Ofloxacin and Cefixime in pharmaceutical formulation in presence of degradation products. The chromatographic separation of Ofloxacin and Cefixime was achieved on Shimadzu LC-20AT series HPLC having C18-ODS bonded column (250 x 4.6 mm, 40 °C, 10 µL) using UV/Visible detector at 276 nm. The optimized mobile phase was consisted of a methanol: phosphate buffer (50:50) at a flow rate of 1.0 ml/m. The retention times were 4.799 and 1.602 m for Ofloxacin and Cefixime respectively. The proposed method provided linear responses within the concentration ranges 5-25 µg/ml for Ofloxacin and Cefixime both. The limit of detection (LOD) and limit of quantification (LOQ) values were found to be 0.0259, 0.078 µg/ml and 0.0206, 0.062 µg/ml for Ofloxacin and Cefixime F respectively. The developed method was validated as per ICH guidelines with respect to specificity, linearity, accuracy, precision, robustness and ruggedness. The studies data revealed that developed method was convenient, fairly reliable, sensitive, less expensive and reproducible.

A sensitive and selective liquid chromatography mass spectrometry method for simultaneous estimation of anti-diabetic drugs inhibiting DPP-4 enzyme in human plasma: overcoming challenges associated with low recovery and sensitivity

A simple and sensitive LC-QTOF/MS method was developed and validated to measure the human plasma concentrations of five gliptins.

Colorimetric estimation of human glucose level using γ-Fe2O3 nanoparticles: An easily recoverable effective mimic peroxidase

This article reports simple, green and efficient synthesis of γ-Fe2O3 nanoparticles (NPs) (maghemite) through single-source precursor approach for colorimetric estimation of human glucose level. The γ-Fe2O3 NPs, having cubic morphology with an average particle size of 30nm, exhibited effective peroxidase-like activity through the catalytic oxidation of peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2 producing a blue-colored solution. On the basis of this colored-reaction, we have developed a simple, cheap, highly sensitive and selective colorimetric method for estimation of glucose using γ-Fe2O3/TMB/glucose–glucose oxidase (GOx) system in the linear range from 1 to 80μM with detection limit of 0.21μM. The proposed glucose sensor displays faster response, good stability, reproducibility and anti-interference ability. Based on this simple reaction process, human blood and urine glucose level can be monitored conveniently.

The relevance of innovation leadership for environmental benefits: A firm-level empirical analysis on French firms

This paper seeks to contribute to the green building debate in economics and management by focusing on environmental innovation and innovation leadership. The latter is the dynamic capability of an innovative firm to seize new innovation opportunities as a result of a proactive investment policy and enhanced innovativeness. The paper defends the thesis according to which firms that are consistently “innovation leaders” are those that encourage environmental innovations. We use French CIS Surveys and employ a Heckman selection estimation method using a sample of 1180 firms to study which different forms of innovation leadership increase the propensity to develop environmental innovations. We find a strong impact of innovation leadership that is measured in a novel way, using innovation persistence. Furthermore, the results show a strong impact of regulations and costs savings as determinants of eco-innovation.

Set Predicates in SQL: Enabling Set-Level Comparisons for Dynamically Formed Groups

In data warehousing and OLAP applications, scalar-level predicates in SQL become increasingly inadequate to support a class of operations that require set-level comparison semantics, i.e., comparing a group of tuples with multiple values. Currently, complex SQL queries composed by scalar-level operations are often formed to obtain even very simple set-level semantics. Such queries are not only difficult to write but also challenging for a database engine to optimize, thus can result in costly evaluation. This paper proposes to augment SQL with set predicate, to bring out otherwise obscured set-level semantics. We studied two approaches to processing set predicates-an aggregate function-based approach and a bitmap index-based approach. Moreover, we designed a histogram-based probabilistic method of set predicate selectivity estimation, for optimizing queries with multiple predicates. The experiments verified its accuracy and effectiveness in optimizing queries.

Rapid and Selective LC method for estimation of Duloxitine Hydrochloride

The Duloxitine Hydrochloride was estimated by using a HPLC method. It was separated on a Waters symmetry C8 HPLC column (250 × 4.6 mm, 5μ) by passing mobile phase at a flow rate of 1.0 ml/min and the solution was monitored at a wavelength of 288nm. The retention time of the duloxitine was found to be 7.39 min. The developed method was validated according to ICH guidelines. The developed method was accurate, precise and linear. This method can be successfully applied in quality control laboratories for routine analysis of duloxitine in pharmaceutical formulations.

Cormorant Catch Concerns for Fishers: Estimating the Size-Selectivity of a Piscivorous Bird

Conflict arises in fisheries worldwide when piscivorous birds target fish species of commercial value. This paper presents a method for estimating size selectivity functions for piscivores and uses it to compare predation selectivities of Great Cormorants (Phalacrocorax carbo sinensis L. 1758) with that of gill-net fishing on a European perch (Perca fluviatilis L. 1758) population in the Curonian Lagoon, Lithuania. Fishers often regard cormorants as an unwanted “satellite species”, but the degree of direct competition and overlap in size-specific selectivity between fishers and cormorants is unknown. This study showed negligible overlap in selectivity between Great Cormorants and legal-sized commercial nets. The selectivity estimation method has general application potential for use in conjunction with population dynamics models to assess fish population responses to size-selective fishing from a wide range of piscivorous predators.

Validation of chiral liquid chromatography-tandem mass spectrometric method for the estimation of bicalutamide enantiomers in human plasma: application to a bioequivalence study

Bicalutamide (BCT) is a non-steroidal antiandrogen used for the treatment of prostate cancer. Its chemical name is ( RS )-N-[4-cyano-3-(trifluoromethyl) phenyl]-3-[(4-fluorophenyl) sulfonyl]-2-hydroxy-2-methyl-propanamide. BCT as such is a racemic mixture, but most of its pharmacological activity is attributed to its R enantiomer. A single, simple and selective method for simultaneous estimation of (-)-BCT and (+)-BCT in human plasma was validated using (-)-d4-BCT and (+)-d4-BCT as internal standards. The compounds were separated on a Chiralpak AD-3R column under isocratic conditions consisting of 5mM ammonium acetate buffer and methanol (70:30, v/v), with a total run time of 6.5 minutes and detected by tandem mass spectrometry with negative ionization mode. The ion transitions recorded in multiple reaction monitoring mode were m/z 429.0a185.0 for BCT enantiomers and m/z 433.0a185.0 for d4-BCT enantiomers. Linearity in plasma was observed over the concentration range 10.0 – 3000.0 ng/mL for (-)-BCT and 2.0 – 200.0 ng/mL for (+)-BCT. The mean recovery was 81.2 % and 78.0 % for (-)-BCT and (+)-BCT respectively. The coefficient of variation of the assay was less than 4.2 % and 6.8 % for (-)-BCT and (+)-BCT with an accuracy of 99.3 % to 104.1 % and 98.6 % to 103.4 % for (-)-BCT and (+)-BCT respectively. Stability was evaluated under different conditions including bench top, processed sample, freeze and thaw, autosampler and long term. The validated method was applied for the determination of individual BCT enantiomers in human plasma samples from a bioequivalence study of 150mg fixed dose formulation in 12 healthy Indian subjects. Assay reproducibility was demonstrated by reanalysis of 10% incurred samples.

Comparison of estimators of the Gumbel distribution for modelling annual maximum rainfall

The estimation of extreme rainfall for a desired return period is of utmost importance for planning, design and management of hydraulic and other structures in a region. This paper presents the methodology adopted in rainfall estimation for Hissar and Kalingapatnam regions using six parameter estimation methods of Gumbel distribution. The Kolmogorov–Smirnov (KS) statistic is used for checking the adequacy of fitting of the method for determination of estimators of the distribution. Diagnostic tests involving D-index and root mean square error are used for the selection of a suitable method for estimation of rainfall. The paper demonstrates that the method of least squares (MLS) is better suited for modelling annual maximum rainfall for Hissar and probability weighted moments (PWM) for Kalingapatnam. The KS test results and diagnostic analysis show that the 1000 year return period extreme rainfalls given by MLS and PWM may be adopted for design purposes in the Hissar and Kalingapatnam regions respectively.

Development and validation of highly selective and robust method for simultaneous estimation of pioglitazone, hydroxypioglitazone and metformin in human plasma by LC–MS/MS: Application to a pharmacokinetic study

A simple, selective and robust reverse phase high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (ESI-MS/MS) method for simultaneous quantitation of pioglitazone (PIO), pioglitazone metabolite M-IV - hydroxypioglitazone (OH-PIO) and metformin (MET) in human plasma using deuterated internal standards (IS) is developed and fully validated as per industrial practices. After acetonitrile-induced protein precipitation of the plasma samples; PIO, OH-PIO, MET and IS were chromatographed on reverse phase column and analyzed in the multiple reaction monitoring in positive ion mode. The ion transitions were monitored at m/z 357.2→134.2 for PIO, 373.0→150.1 for OH-PIO, 130.2→71.0 for MET, 361.1→134.2 for PIO-IS and 136.1→77.1 for MET-IS. The total chromatographic run time was 4.0min. A linear response function (r>0.998) was established for the range of concentrations 15-2500ng/mL, 10-1500ng/mL and 25-3000ng/mL for PIO, OH-PIO and MET respectively in human plasma. The intra and inter-day precision and accuracy values have met the set acceptance criteria. The method is simple, selective, robust economic and has been applied successfully to more than 2000 plasma samples as part of pharmacokinetic study in humans.

An SAD-Based Selective Bi-prediction Method for Fast Motion Estimation in High Efficiency Video Coding

As the next-generation video coding standard, High Efficiency Video Coding (HEVC) has adopted advanced coding tools despite the increase in computational complexity. In this paper, we propose a selective bi-prediction method to reduce the encoding complexity of HEVC. The proposed method evaluates the statistical property of the sum of absolute differences in the motion estimation process and determines whether bi-prediction is performed. A performance comparison of the complexity reduction is provided to show the effectiveness of the proposed method compared to the HEVC test model version 4.0. On average, 50% of the bi-prediction time can be reduced by the proposed method, while maintaining a negligible bit increment and a minimal loss of image quality.

Guidelines for a graph‐theoretic implementation of structural equation modeling

Structural equation modeling (SEM) is increasingly being chosen by researchers as a framework for gaining scientific insights from the quantitative analyses of data. New ideas and methods emerging from the study of causality, influences from the field of graphical modeling, and advances in statistics are expanding the rigor, capability, and even purpose of SEM. Guidelines for implementing the expanded capabilities of SEM are currently lacking. In this paper we describe new developments in SEM that we believe constitute a third‐generation of the methodology. Most characteristic of this new approach is the generalization of the structural equation model as a causal graph. In this generalization, analyses are based on graph theoretic principles rather than analyses of matrices. Also, new devices such as metamodels and causal diagrams, as well as an increased emphasis on queries and probabilistic reasoning, are now included. Estimation under a graph theory framework permits the use of Bayesian or likelihood methods. The guidelines presented start from a declaration of the goals of the analysis. We then discuss how theory frames the modeling process, requirements for causal interpretation, model specification choices, selection of estimation method, model evaluation options, and use of queries, both to summarize retrospective results and for prospective analyses.The illustrative example presented involves monitoring data from wetlands on Mount Desert Island, home of Acadia National Park. Our presentation walks through the decision process involved in developing and evaluating models, as well as drawing inferences from the resulting prediction equations. In addition to evaluating hypotheses about the connections between human activities and biotic responses, we illustrate how the structural equation (SE) model can be queried to understand how interventions might take advantage of an environmental threshold to limit Typha invasions.The guidelines presented provide for an updated definition of the SEM process that subsumes the historical matrix approach under a graph‐theory implementation. The implementation is also designed to permit complex specifications and to be compatible with various estimation methods. Finally, they are meant to foster the use of probabilistic reasoning in both retrospective and prospective considerations of the quantitative implications of the results.

Iron selenide thin film: Peroxidase-like behavior, glucose detection and amperometric sensing of hydrogen peroxide

Abstract Iron selenide (FeSe) thin film was deposited on glass or indium doped tin oxide (ITO) coated glass substrates through chemical bath deposition process from a precursor complex, [Fe 3 (μ 3 -O)(μ 2 -O 2 CCH 2 Cl) 6 (H 2 O) 3 ]NO 3 ·H 2 O and was characterized by X-ray diffraction, field emission scanning electron microscopy and UV–vis spectroscopic techniques. Structural analyses revealed that the FeSe film had spherical morphology with average diameter of 30 nm. The film was shown to possess peroxidase-like catalytic activity toward oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 and followed Michaelis–Menten kinetics. It was exploited as a simple and cheap material in selective colorimetric method for detection and estimation of glucose in buffer solution. It gave a linear response to glucose over the concentration range from 2 × 10 −6 to 3 × 10 −5 M with a detection limit of 5 × 10 −7 M. Furthermore, the FeSe film, deposited on ITO, performed as good amperometric sensors for detection of H 2 O 2 . To compare the catalytic and sensing efficiency of the FeSe film, we have also prepared FeS film under similar conditions.

Semiparametric Estimation of Additive Quantile Regression Models by Two-Fold Penalty

In this article, we propose a model selection and semiparametric estimation method for additive models in the context of quantile regression problems. In particular, we are interested in finding nonzero components as well as linear components in the conditional quantile function. Our approach is based on spline approximation for the components aided by two Smoothly Clipped Absolute Deviation (SCAD) penalty terms. The advantage of our approach is that one can automatically choose between general additive models, partially linear additive models, and linear models in a single estimation step. The most important contribution is that this is achieved without the need for specifying which covariates enter the linear part, solving one serious practical issue for models with partially linear additive structure. Simulation studies as well as a real dataset are used to illustrate our method.

Asymptotically error-optimal shape of sampling zone for query selectivity estimation method based on discrete cosine transform

The problem of query selectivity estimation for database queries is critical for efficient query execution by database management systems. A query execution method strongly depends on early estimated size of a query result. This estimation determines a data access method used later during the query execution. The selectivity parameter is a fraction of table rows that satisfy a single-table query condition. For a selection condition of a range query where an attribute has a continuous domain, the selectivity is equivalent to a definite integral form probability density function (PDF) of attribute values distribution. For a compound selection condition based on many attributes we need a multidimensional space-efficient non-parametric estimator of multivariate PDF of attribute values distribution. A known approach based on Discrete Cosine Transform (DCT) spectrum as an representation of multidimensional PDF is considered. The energy compaction property of DCT lets omit a region of spectrum coefficients with small absolute values without significant losing an accuracy of selectivity estimation. An area of relevant spectrum coefficients is called a sampling zone. Results of experiments from previous works shows that applying the reciprocal shape of the sampling zone gives the least selectivity estimation error subject to a predetermined size of the zone. The main result of this work is a theoretical confirmation of only experimental results from previous works. The paper presents the proof of the theorem that the reciprocal shape of the sampling zone is asymptotically error-optimal. The proof is based on calculus of variations and the isoperimetric problem.

A sensitive and selective HPLC method for estimation of lamotrigine in human plasma and saliva: application to plasma-saliva correlation in epileptic patients

A sensitive and selective high performance liquid chromatographic (HPLC) method was developed and validated for estimation of lamotrigine (CAS 84057-84-1) in human plasma and saliva. The chromatographic separation was achieved with a reversed phase column and a mobile phase consisting of acetonitrile and 20 mM ammonium acetate buffer pH 6.5 (30:70) with a flow rate of 1 mL/min. The calibration curve was linear within the working range for both plasma and saliva. The validated method has been successfully applied for a study of lamotrigine in human plasma and saliva to establish the correlation between these two matrices. A scatter plot of plasma versus salivary lamotrigine concentrations showed a gold linear relationship between them (Pearson correlation coefficient, r = 0.6832, p < 0.001).