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A menu-driven facility for complex sample size calculation in randomized controlled trials with a survival or a binary outcome AgEcon
Royston, Patrick; Babiker, Abdel.
We present a menu-driven Stata program for the calculation of sample size or power for complex clinical trials with a survival time or a binary outcome. The features supported include up to six treatment arms, an arbitrary time-to-event distribution, fixed or time-varying hazard ratios, unequal patient allocation, loss to follow-up, staggered patient entry, and crossover of patients from their allocated treatment to an alternative treatment. The computations of sample size and power are based on the logrank test and are done according to the asymptotic distribution of the logrank test statistic, adjusted appropriately for the design features.
Tipo: Journal Article Palavras-chave: Randomized controlled trials; Survival analysis; Logrank test; Experimental design; Research Methods/ Statistical Methods.
Ano: 2002 URL: http://purl.umn.edu/115958
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A Software Package and Hardware Tools for in situ Experiments in a Lagrangian Reference Frame ArchiMer
Doglioli, Andrea; Nencioli, Francesco; Petrenko, Anne; Rougier, Gilles; Fuda, Jean-luc; Grima, Nicolas.
The Lagrangian Transport Experiment (LATEX) was developed to study the influence of coupled physical and biogeochemical dynamics at the meso- and submesoscales on the transfers of matter and heat between the coastal zone and the open ocean. One of the goals of the Latex10 field experiment, conducted during September 2010 in the Gulf of Lion (northwest Mediterranean), was to mark a dynamical mesoscale feature by releasing a passive tracer [sulfur hexafluoride (SF6)] together with an array of Lagrangian buoys. The goal was to release the tracer in an initial patch as homogeneous as possible in the horizontal, and to study its turbulent mixing and dispersion while minimizing the contribution due to advection. For that, it was necessary to continuously adjust...
Tipo: Text Palavras-chave: Dispersion; Lagrangian circulation; Transport; Ship observations; Tracers; Experimental design; Software.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00155/26590/24719.pdf
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Adaptive Experimental Design Using the Propensity Score AgEcon
Hahn, Jinyong; Hirano, Keisuke; Karlan, Dean S..
Many social experiments are run in multiple waves, or are replications of earlier social experiments. In principle, the sampling design can be modified in later stages or replications to allow for more efficient estimation of causal effects. We consider the design of a two-stage experiment for estimating an average treatment effect, when covariate information is available for experimental subjects. We use data from the first stage to choose a conditional treatment assignment rule for units in the second stage of the experiment. This amounts to choosing the propensity score, the conditional probability of treatment given covariates. We propose to select the propensity score to minimize the asymptotic variance bound for estimating the average treatment...
Tipo: Working or Discussion Paper Palavras-chave: Experimental design; Propensity score; Efficiency bound; Research Methods/ Statistical Methods; C1; C14; C9; C93; C13.
Ano: 2009 URL: http://purl.umn.edu/47107
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Agent-based Analysis of Agricultural Policies: an Illustration of the Agricultural Policy Simulator AgriPoliS, its Adaptation and Behavior Ecology and Society
Happe, Kathrin; Leibniz Institute of Agricultural Development in Central and Eastern Europe; happe@iamo.de; Kellermann, Konrad; Leibniz Institute of Agricultural Development in Central and Eastern Europe; kellermann@iamo.de; Balmann, Alfons; Leibniz Institute of Agricultural Development in Central and Eastern Europe; balmann@iamo.de.
This paper combines agent-based modeling of structural change with agricultural policy analysis. Using the agent-based model AgriPoliS, we investigate the impact of a regime switch in agricultural policy on structural change under various framework conditions. Instead of first doing a sensitivity analysis to analyze the properties of our model and then examining the introduced policy in an isolated manner, we use a meta-modeling approach in combination with the statistical technique of Design of Experiments to systematically analyze the relationship between policy change and model assumptions regarding key determinants of structural change such as interest rates, managerial abilities, and technical change. As a result, we observe that the effects of...
Tipo: Peer-Reviewed Reports Palavras-chave: Agent-based modeling; Agricultural policy analysis; Empirical-based simulation; Experimental design; Farm structures; Meta-modeling..
Ano: 2006
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An Assessment of the Precision and Confidence of Aquatic Eddy Correlation Measurements ArchiMer
Donis, Daphne; Holtappels, Moritz; Noss, Christian; Cathalot, Cecile; Hancke, Kasper; Polsenaere, Pierre; Wenzhoefer, Frank; Lorke, Andreas; Meysman, Filip J. R.; Glud, Ronnie N.; Mcginnis, Daniel F..
The quantification of benthic fluxes with the aquatic eddy correlation (EC) technique is based on simultaneous measurement of the current velocity and a targeted bottom water parameter (e.g., O2, temperature). High-frequency measurements (64 Hz) are performed at a single point above the seafloor using an acoustic Doppler velocimeter (ADV) and a fast-responding sensor. The advantages of aquatic EC technique are that 1) it is noninvasive, 2) it integrates fluxes over a large area, and 3) it accounts for in situ hydrodynamics. The aquatic EC has gained acceptance as a powerful technique; however, an accurate assessment of the errors introduced by the spatial alignment of velocity and water constituent measurements and by their different response times is...
Tipo: Text Palavras-chave: Turbulence; Boundary layer; Fluxes; Instrumentation/sensors; Optimization; Experimental design.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00275/38577/37102.pdf
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Analysis of experiments in square lattice with emphasis on variance components. i. Individual analysis PAB
Silva,Heyder Diniz; Regazzi,Adair José; Cruz,Cosme Damião; Viana,José Marcelo Soriano.
This paper focused on four alternatives of analysis of experiments in square lattice as far as the estimation of variance components and some genetic parameters are concerned: 1) intra-block analysis with adjusted treatment and blocks within unadjusted repetitions; 2) lattice analysis as complete randomized blocks; 3) intrablock analysis with unadjusted treatment and blocks within adjusted repetitions; 4) lattice analysis as complete randomized blocks, by utilizing the adjusted means of treatments, obtained from the analysis with recovery of interblock information, having as mean square of the error the mean effective variance of this same analysis with recovery of inter-block information. For the four alternatives of analysis, the estimators and estimates...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Experimental design; Genetic parameters; Plant breeding.
Ano: 1999 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-204X1999001000007
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Assessment of oxidation of leaves of Ilex paraguariensis (St. Hil) BABT
Molin,Rochele Fernanda; Valduga,Alice Teresa; Di Luccio,Marco; Dartora,Nessana; Cichoski,Alexandre José; Pistore,Mônica; Rigo,Elisandra.
This work aimed to study the oxidation of leaves of Ilex paraguariensis St. Hil, in a process similar to the oxidation of Camellia sinensis, with the purpose of developing new products based on yerba maté. So far, no previous systematic study about the oxidation of yerba maté has been found elsewhere. A Plackett-Burman experimental design was used for the screening of the significant parameters that affected the oxidation. The oxidation was indirectly quantified by following the changes in the product color, water activity, and pH with the time of processing. The factors that most influenced the process were the age of the leaves and the relative humidity of the oxidation chamber. The differences between the treatments were more evident after 3, 6 12 and...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Physicochemical parameters; Yerba maté; Leave; Extract; Experimental design.
Ano: 2011 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132011000200016
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Chiral discrimination of amlodipine from pharmaceutical products using capillary electrophoresis BJPS
Cârcu-Dobrin,Melania; Sabău,Alexandra Georgiana; Hancu,Gabriel; Árpád,Gyéresi; Rusu,Aura; Kelemen,Hajnal; Papp,Lajos Attila; Cârje,Anca.
The present work describes the development of a capillary electrophoresis (CE) method for the chiral discrimination of amlodipine (AML) enantiomers using cyclodextrine (CD) derivatives as chiral selectors. A large number of native and derivatized, neutral and ionized CD derivatives were screened to find the optimal chiral selector; and carboximethyl-β-CD (CM-β-CD) was selected for the enantiomeric discrimination. A factorial analysis study was performed by orthogonal experimental design in which several factors were varied at the same time to optimize the separation method. The optimized method (25 mM phosphate buffer, pH = 9.0, 15 mM CM-β-CD, 15 ºC, + 25 kV, 30 mbar/1 second, detection wavelength 230 nm) was successfully applied for the baseline...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Amlodipine; Capillary electrophoresis; Chiral separation; Cyclodextrine; Experimental design.
Ano: 2020 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1984-82502020000100530
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Comparison of analyses types in carrot experiment: square lattice versus randomized blocks design Horticultura Brasileira
Carvalho,Agnaldo DF; Silva,Giovani O.
ABSTRACT The square lattice 4x4 design was compared to a randomized block design, for carrot F1 hybrids. Sixteen experimental carrot hybrids were evaluated in Brasília, in 2014/15 and 2015/16 agricultural years. A square lattice 4x4 design with three replications was used. The experimental plot consisted of 1.5 m2 useful area. The experimental area was installed on the second half of November 2014 and 2015. Cultural practices were the usually given to the carrot crop in Brazilian savannah region. The incidence of leaf blight was evaluated 90 days after sowing date and, after 100 days, roots were harvested and yield components evaluated. We evaluated the three possible analyses in lattice: 1) as randomized block design; 2) intrablock analysis with adjusted...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Daucus carota; Experimental design; Incomplete block.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0102-05362018000200217
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Development of a generic method for the determination of proton-pump inhibitors by capillary zoneelectrophoresis BJPS
Papp,Lajos Attila; Gyéresi,Árpád; Hancu,Gabriel; Mircia,Eleonora; Kelemen,Hajnal.
A generic capillary zone electrophoresis method was developed for the analysis of four proton pump inhibitors: omeprazole, pantoprazole, lansoprazole and rabeprazole. During preliminary analysis screening of phosphate buffers at different pH levels was performed, in order to determine the optimum pH domain suitable for the simultaneous determination of all studied compounds. A face centered central composite design was employed for the optimization of separation conditions. The effect of buffer concentration, pH and applied voltage was studied; resolution between peaks and migration time of the last compound were considered as responses. Other factors as system temperature, injection parameters, capillary length, were held constant during the optimization...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Capillary electrophoresis; Proton-pump inhibitors; Experimental design.
Ano: 2019 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1984-82502019000100534
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Do different sampling designs produce differences in the metrics of curimba, Prochilodus lineatus (Characiformes: Prochilodontidae)? Neotropical Ichthyology
Kurchevski,Gregório; Godinho,Alexandre Lima.
ABSTRACT Probabilistic sampling, a classical recommendation for unbiased data, has been often overlooked. Fish sampling in reservoirs, unlike most rivers, can be accomplished by a variety of probabilistic sampling designs due to few restrictions in the choice of sampling sites (SSs). We evaluated whether population metrics of Prochilodus lineatus differ between fixed SSs (do not change with each sampling trip) and variable SSs (change with each sampling trip) in the Volta Grande (VGR) and Jaguara (JR) reservoirs of the Grande River, Paraná River basin, Brazil. We used gillnets to sample fish at nine probabilistic fixed SSs and nine probabilistic variable SSs per sampling trip. We conducted 25 sampling trips in VGR and 22 in JR during 2011 to 2015, and...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Experimental design; Fixed versus variable sampling sites; Grande River basin; Probabilistic sampling; Reservoir.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1679-62252018000400216
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Efficiency benefits of choice model experimental design updating: a case study AgEcon
Kerr, Geoffrey N.; Sharp, Basil M.H..
Efficient experimental designs offer the potential to reduce confidence intervals for parameters of interest in choice models, or to reduce required sample sizes. C-efficiency recognises the salience of willingness to pay estimates rather than utility function parameters. This study reports on a choice model application that incorporated updated statistical designs based on initial responses in order to maximise C-efficiency. The revised design delivered significant improvements.
Tipo: Conference Paper or Presentation Palavras-chave: Experimental design; Choice experiment; Efficiency; Research Methods/ Statistical Methods.
Ano: 2009 URL: http://purl.umn.edu/47623
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Efficient design for willingness to pay in choice experiments: evidence from the field AgEcon
Kerr, Geoffrey N.; Sharp, Basil M.H..
Efficient experimental designs offer the potential to reduce confidence intervals for parameters of interest in choice models, or to reduce required sample sizes. C-efficiency recognizes the salience of willingness to pay estimates rather than utility function parameters. This study reports on a choice model application that incorporated updated statistical designs based on initial responses in order to maximize C-efficiency. The revised design delivered significant improvements.
Tipo: Conference Paper or Presentation Palavras-chave: Experimental design; Choice experiment; Efficiency; Environmental Economics and Policy; Research Methods/ Statistical Methods.
Ano: 2009 URL: http://purl.umn.edu/97156
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Estimating variance components in Stata AgEcon
Marchenko, Yulia V..
This article gives a brief overview of the popular methods for estimating variance components in linear models and describes several ways to obtain such estimates in Stata for various experimental designs. The article’s emphasis is on using xtmixed to estimate variance components. Prior to Stata 9, loneway could be used to estimate variance components for one-way random-effects models. For other experimental designs, variance components could be computed manually using saved results after anova. The latter approach is viable but requires tedious computations for complicated experimental designs. Instead, as of Stata 9, variance components are easily obtained by using xtmixed.
Tipo: Journal Article Palavras-chave: Variance components; Experimental design; ANOVA; REML; ML; Multilevel; Random coefficients; Mixed models; Research Methods/ Statistical Methods.
Ano: 2005 URL: http://purl.umn.edu/117553
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Evaluation of process parameters in the industrial scale production of fish nuggets Ciênc. Tecnol. Aliment.
Silva,Adriane da; Zitkoski,João; Mazutti,Marcio Antônio; Mossi,Altemir; Oliveira,José Vladimir; Oliveira,Débora de; Cichoski,Alexandre José; Treichel,Helen.
This work reports the use of experimental design for the assessment of the effects of process parameters on the production of fish nuggets in an industrial scale environment. The effect of independent factors on the physicochemical and microbiological parameters was investigated through a full 24 experimental design. The studied factors included the temperature of fish fillet and pulp in the mixer, the temperature of the added fat, the temperature of water and the ratio of protein extraction time to emulsion time. The physicochemical analyses showed that the higher temperature of the pulp and fillet of fish, the lower the protein in the final product. Microbiological analyses revealed that the counting of Staphylococcus coagulase positive, total and...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Fish nuggets; Experimental design; Process parameters.
Ano: 2011 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0101-20612011000200019
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Extraction of red cabbage anthocyanins: optimization of the operation conditions of the column process BABT
Xavier,Marcelo Fonseca; Lopes,Toni Jefferson; Quadri,Mara Gabriela Novy; Quadri,Marintho Bastos.
The aim of this work was to extract anthocyanins from the red cabbage. Batch studies under several extraction conditions indicated that acetic acid in aqueous solution (10% V/V) was the best solvent, used in the proportion of 0.25 g of red cabbage mL-1. At this condition, column assays were carried out to evaluate the influence of the ionic force, pH, solvent flow rate, recirculated volume of red cabbage juice and the mass of red cabbage. Results showed that the pH, recirculation and mass of red cabbage had statistically significant effects, where the optimum operation conditions found for the process were pH 2.3, recirculation volume of the solvent 0.83 L and mass of red cabbage 50 g.
Tipo: Info:eu-repo/semantics/article Palavras-chave: Anthocyanins; Extraction; Red cabbage; Experimental design; Optimization.
Ano: 2008 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132008000100018
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Factors affecting the performance of Pantaneiro horses R. Bras. Zootec.
Souza,Geraldo da Silva e; Gomes,Eliane Gonçalves; Santos,Sandra Aparecida; Rezende,Adalgiza Souza Carneiro de; Andrade,Débora Roque de Freitas; Nogueira,Márcia Furlan; Trigo,Pablo; Abreu,Urbano Gomes Pinto de.
ABSTRACT This study aimed to assess the physical performance of Pantaneiro horses with and without equine infectious anemia (EIA) under functional conditions of cattle management. The horses were subjected to a performance test and split into two groups according to a completely randomized design: animals were chosen from populations testing positive and negative for EIA. Performance was measured as a function of a data envelopment analysis (DEA) model considering four outputs and one unitary input. The output measures were the distance achieved in the performance test, hematocrit as a weighted average over the test duration, respiratory rate as weighted average over the test duration, and the level of lactic acid at the test termination. Weights for the...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Covariance analysis; Data envelopment analysis; Equine infectious anaemia; Experimental design; Multivariate analysis.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-35982018000100502
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Head Space Solid Phase Micro-Extraction (HS - SPME) of volatile organic compounds produced by Sporidiobolus salmonicolor (CBS 2636) Ciênc. Tecnol. Aliment.
Valduga,Eunice; Valerio,Alexsandra; Treichel,Helen; Nascimento Filho,Irajá; Fúrigo Júnior,Agenor; Di Luccio,Marco.
The aim of the present study was the assessment of volatile organic compounds produced by Sporidiobolus salmonicolor (CBS 2636) using methyl and ethyl ricinoleate, ricinoleic acid and castor oil as precursors. The analysis of the volatile organic compounds was carried out using Head Space Solid Phase Micro-Extraction (HS - SPME). Factorial experimental design was used for investigating extraction conditions, verifying stirring rate (0-400 rpm), temperature (25-60 ºC), extraction time (10-30 minutes), and sample volume (2-3 mL). The identification of volatile organic compounds was carried out by Gas Chromatography with Mass Spectrum Detector (GC/MSD). The conditions that resulted in maximum extraction were: 60 ºC, 10 minutes extraction, no stirring, sample...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Bio-production; Sporidiobolus salmonicolor; SPME; Aroma; Experimental design.
Ano: 2010 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0101-20612010000400023
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Herbicide selectivity by differential metabolism: considerations for reducing crop damages Scientia Agricola
Carvalho,Saul Jorge Pinto de; Nicolai,Marcelo; Ferreira,Renato Rodrigues; Figueira,Antonio Vargas de Oliveira; Christoffoleti,Pedro Jacob.
Herbicide selectivity is an agricultural technology largely exploited in chemical strategies of weed control. The joint action of several protection mechanisms avoids phytotoxicity from herbicide treatment, maintaining the level of agronomically accepted damage to a minimum, or even totally avoiding them. The major mechanism of herbicide selectivity derives from the differential metabolism between weed and crop plant species, with weeds presenting a limited ability to perform it under agronomically recommended conditions. In this case, phytotoxicity can be interpreted as an overcoming of the maximum protection capacity offered by the mechanisms of selectivity, or when considering metabolism as the main factor, the overcoming of the inherent plant ability...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Phytotoxicity; Injuries; Yield; Experimental design; Crop management.
Ano: 2009 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162009000100020
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High levels of β-xylosidase in Thermomyces lanuginosus: potential use for saccharification BJM
Corrêa,Juliana Moço; Christi,Divair; Torre,Carla Lieko Della; Henn,Caroline; Conceição-Silva,José Luis da; Kadowaki,Marina Kimiko; Simão,Rita de Cássia Garcia.
ABSTRACT A new strain of Thermomyces lanuginosus was isolated from the Atlantic Forest biome, and its β-xylosidases optimization in response to agro-industrial residues was performed. Using statistical approach as a strategy for optimization, the induction of β-xylosidases activity was evaluated in residual corn straw, and improved so that the optimum condition achieved high β-xylosidases activities 1003 U/mL. According our known, this study is the first to show so high levels of β-xylosidases activities induction. In addition, the application of an experimental design with this microorganism to induce β-xylosidases has not been reported until the present work. The optimal conditions for the crude enzyme extract were pH 5.5 and 60 °C showing better...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Experimental design; Saccharification; Β-Xylosidase; Thermomyces lanuginosus; Atlantic Forest.
Ano: 2016 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1517-83822016000300680
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