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A menu-driven facility for complex sample size calculation in randomized controlled trials with a survival or a binary outcome: Update AgEcon
Barthel, Friederike Maria-Sophie; Royston, Patrick; Babiker, Abdel.
Royston and Babiker (2002) presented a menu-driven Stata program for the calculation of sample size or power for complex clinical trial designs under a survival time or binary outcome. In the present article, the package is updated to Stata 8 under the new name ART. Furthermore, the program has been extended to incorporate noninferiority designs and provides more detailed output. This package is the only realistic sample size tool for survival studies available in Stata.
Tipo: Journal Article Palavras-chave: Sample size; Power; Randomized controlled trial; Multiarm designs; Survival analysis; Research Methods/ Statistical Methods.
Ano: 2005 URL: http://purl.umn.edu/117503
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Calidad sanitaria en la producción de nopal verdura (Opuntia sp.) en Otumba, México. Colegio de Postgraduados
Martínez Martínez, Talina Olivia.
La calidad sanitaria en los productos hortofrutícolas debe considerarse una prioridad en la producción de alimentos. Actualmente en México, existe una gran preocupación por las asociaciones de productores y gobierno federal para adoptar sistemas de producción que reduzcan riesgos de contaminación (SRRC). Para la implementación de estos sistemas, es necesario cumplir con una serie de requisitos, entre ellos se encuentra la validación de procesos. Un método inmediato para efectuar este requerimiento, es la evaluación de la calidad sanitaria desde el punto de vista microbiológico y toxicológico, lo que hace necesario determinar un plan de muestreo y las técnicas apropiadas para la detección y cuantificación de patógenos indicadores. Con este propósito, en...
Palavras-chave: Salmonella; Escherichia coli; Pesticides; Phenolic compounds; Survival; Sample size; Entomología y Acarología; Doctorado.
Ano: 2011 URL: http://hdl.handle.net/10521/590
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Comparison of beat cloth and entomological net methods for determining faunistic indices of soybean in Rio Grande do Sul, Brazil Scientia Agricola
Storck,Lindolfo; Antúnez,Claudia Carolina Cabral; Guedes,Jerson Vanderlei Carús; Cargnelutti Filho,Alberto; Alvarez,Jimmy Walter Rasche.
ABSTRACT Estimates of diversity indices provide information on distribution, richness and abundance of species within a community. The aim of the current study was to estimate faunistic indices (richness, constancy, dominance and abundance) of the species collected by beat cloth and entomological net sampling methods in different soybean crops and to determine the sample size necessary to estimate faunistic indices. Fauna density from 100 soybeans crops located in nine municipalities in Rio Grande do Sul, Brazil, were evaluated. Thirty points, 20 meters apart from one another, were marked in the crops. At each point, insect pests and natural enemies were collected using the two sampling methods. Faunistic indices, including the average and interval...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Glycine max; Resampling; Sample size; Natural enemies; Sampling methods.
Ano: 2016 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162016000600559
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Differences in performance among four indices used to evaluate diversity in planktonic ecosystems ArchiMer
Beaugrand, G; Edwards, M.
The performance of four common estimators of diversity are investigated using calanoid copepod data from the Continuous Plankton Recorder (CPR) survey. The region of the North Atlantic and the North Sea was divided into squares of 400 nautical miles for each 2-month period. For each 144 possible cases, Pielou's pooled quadrat method was performed with the aims of determining asymptotic diversity and investigating the CPR sample-size dependence of diversity estimators. It is shown that the performance of diversity indices may greatly vary in space and time (at a seasonal scale). This dependence is more pronounced in higher diverse environments and when the sample size is small. Despite results showing that all estimators underestimate the 'actual'...
Tipo: Text Palavras-chave: Programme continuous plankton recorder; Copépodes; Indices de diversité; Taille de l’échantillonnage; Sensibilité; Continuous Plankton Recorder survey; Copepods; Diversity indices; Sample size; Sensitivity.
Ano: 2001 URL: http://archimer.ifremer.fr/doc/00322/43343/42884.pdf
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Estimativa do tamanho amostral em medidas repetidas de circunferência escrotal de bovinos Nelore. Repositório Alice
FREITAS, A. R. de; SILVA, A. E. D. F. da; UNANIAN, M..
O objetivo deste trabalho foi estimar o tamanho amostral minino (n) de animais pra se detectar diferenca minima significativa entre avaliacoes mensais repetidas da circuferencia escrotal de animais da raca Nelore, dos 10 aos 30 meses de idade, consideradas como 21 condicoes de avaliacao ou medidas repetidas (tratamentos). O valor de n que permite detectar a entre as medias, quando cada individuo e avaliado para t. 2 tratamentos, foi obtido por meio de um programa desenvolvido no statistical Analysis System - SAS, considerando-se o modelo de distribuicao normal t-variada( t=21) com vetor de media zero e matriz de covariancia S, estatistica e distribuicao F com parametro de nao centralidade 2.
Tipo: Separatas Palavras-chave: Escrotal circuferencia; Tamanho amostral; Medidas repetidas; Sample size; Scrotal circumference; Nellore cattle.; Gado de Corte; Gado Nelore.; Beef cattle..
Ano: 1999 URL: http://www.alice.cnptia.embrapa.br/alice/handle/doc/44460
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Power by simulation AgEcon
Feiveson, A.H..
This paper describes how to write Stata programs to estimate the power of virtually any statistical test that Stata can perform. Examples given include the t test, Poisson regression, Cox regression, and the nonparametric rank-sum test.
Tipo: Journal Article Palavras-chave: Power; Simulation; Random number generation; Postfile; Copula; Sample size; Research Methods/ Statistical Methods.
Ano: 2002 URL: http://purl.umn.edu/115955
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REPEATABILITY OF FRUIT QUALITY TRAITS OF CACTUS PEAR Rev. Bras. Frutic.
NUNES,VALTÂNIA XAVIER; NUNES,NÚBIA XAVIER; OLIVEIRA,CARLINNE GUIMARÃES DE; SOBRAL,RAQUEL RODRIGUES SOARES; SANTOS,CARLOS EDUARDO MAGALHÃES DOS.
ABSTRACT Repeatability analysis has been used to study traits in several crops, assisting in the definition of the minimum number needed to evaluate genotypes more efficiently and with less time and resource consumption. So far, however, no repeatability studies on cactus pear have been found in the literature. The objective of this study was to determine the coefficient of repeatability for cactus pear fruits traits and the minimum number of evaluations (fruit) that can provide acceptable accuracy for the prediction of the true value. The experiment was conducted at the Federal Institute of Bahia/Campus Guanambi, with 150 fruits collected from three municipalities in the state of Bahia. The coefficients of repeatability were estimated by the methods of...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Opuntia ficus-indica; Sample size; Components of variance; Phenotypic covariance.
Ano: 2017 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-29452017000500804
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Sample size and power calculations using the noncentral t-distribution AgEcon
Harrison, David A.; Brady, Anthony R..
The standard formulas for sample size and power calculation, as implemented in the command sampsi, make use of a normal approximation to the t-distribution. When the sample sizes are small, this approximation is poor, resulting in overestimating power (or underestimating sample size). One particular situation in which this is likely to be important is the field of cluster randomized trials. Although the total number of individuals in a cluster randomized trial may be large, the number of clusters will often be small. We present a simulation study from the design of a cluster randomized crossover trial that motivated this work and a command to perform more accurate sample size and power calculations based on the noncentral t-distribution.
Tipo: Journal Article Palavras-chave: Sampncti; Sample size; Power; Noncentral t-distribution; Research Methods/ Statistical Methods.
Ano: 2004 URL: http://purl.umn.edu/116234
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Sample size calculations for main effects and interactions in case–control studies using Stata's nchi2 and npnchi2 functions AgEcon
Saunders, Catherine L.; Bishop, D. Timothy; Barrett, Jennifer H..
The non-central chi-squared distribution can be used to calculate power for tests detecting departure from a null hypothesis. Required sample size can also be calculated because it is proportional to the non-centrality parameter for the distribution. We demonstrate how these calculations can be carried out in Stata using the example of calculating power and sample size for case–control studies of gene–gene and gene–environment interactions. Do-files are available for these calculations.
Tipo: Journal Article Palavras-chave: Gene–environment interaction; Gene–gene interaction; Power; Sample size; Study design; Non-central chi^2; Research Methods/ Statistical Methods.
Ano: 2003 URL: http://purl.umn.edu/116031
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Sample size for estimating average productive traits of pigeon pea Ciência Rural
Facco,Giovani; Cargnelutti Filho,Alberto; Alves,Bruna Mendonça; Burin,Cláudia; Santos,Gustavo Oliveira dos; Kleinpaul,Jéssica Andiara; Neu,Ismael Mario Márcio.
ABSTRACT: The objectives of this study were to determine the sample size, in terms of number of plants, needed to estimate the average values of productive traits of the pigeon pea and to determine whether the sample size needed varies between traits and between crop years. Separate uniformity trials were conducted in 2011/2012 and 2012/2013. In each trial, 360 plants were demarcated, and the fresh and dry masses of roots, stems, and leaves and of shoots and the total plant were evaluated during blossoming for 10 productive traits. Descriptive statistics were calculated, normality and randomness were checked, and the sample size was calculated. There was variability in the sample size between the productive traits and crop years of the pigeon pea culture....
Tipo: Info:eu-repo/semantics/article Palavras-chave: Cajanus cajan L.; Sample size; Experimental precision..
Ano: 2016 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-84782016000400619
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Sample size for estimating average trunk diameter and plant height in eucalyptus hybrids Ciência Rural
Cargnelutti Filho,Alberto; Beltrame,Rafael; Bisognin,Dilson Antônio; Lazarotto,Marília; Haselein,Clovis Roberto; Gatto,Darci Alberto; Santos,Gleison Augusto dos.
ABSTRACT: In eucalyptus crops, it is important to determine the number of plants that need to be evaluated for a reliable inference of growth. The aim of this study was to determine the sample size needed to estimate average trunk diameter at breast height and plant height of inter-specific eucalyptus hybrids. In 6,694 plants of twelve inter-specific hybrids it was evaluated trunk diameter at breast height at three (DBH3) and seven years (DBH7) and tree height at seven years (H7) of age. The statistics: minimum, maximum, mean, variance, standard deviation, standard error, and coefficient of variation were calculated. The hypothesis of variance homogeneity was tested. The sample size was determined by re sampling with replacement of 10,000 re samples. There...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Eucalyptus spp.; Number of plants; Sample size; Experimental planning..
Ano: 2016 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-84782016000701192
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Sampling design optimization for EROD measurements in fish ArchiMer
Beliaeff, Benoit; Burgeot, Thierry.
Activity of 7-ethoxyresorufin-O-deethylase (EROD) in fish is certainly the best-studied biomarker of exposure applied in the field to evaluate biological effects of contamination in the marine environment. Since 1991, a feasibility study for a monitoring network using this biomarker of exposure has been conducted along French coasts. Using data obtained during several cruises, this study aims to determine the number of fish required to detect a given difference between 2 mean EROD activities, i.e. to achieve an a priori fixed statistical power (l-beta) given significance level (alpha), variance estimations and projected ratio of unequal sample sizes (k). Mean EROD activity and standard error were estimated at each of 82 sampling stations. The...
Tipo: Text Palavras-chave: Biomonitoring; Estimation; EROD activity; Statistical power; Sample size; Sampling design.
Ano: 1997 URL: http://archimer.ifremer.fr/doc/00337/44787/44483.pdf
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Sampling of cashew nuts as an aid to research for the genetic improvement of cashew tree PAB
Rossetti,Adroaldo Guimarães; Vidal Neto,Francisco das Chagas; Barros,Levi de Moura.
Abstract: The objective of this work was to estimate sample sizes of cashew (Anacardium occidentale) nuts as an aid to the genetic improvement of cashew tree. Nuts were separated by size: nuts < 17 mm were classified as size 1 (S1); 17 mm ≤ nuts < 19 mm, size 2 (S2); 19 mm ≤ nuts < 23 mm, size 3 (S3); 23 mm ≤ nuts < 25 mm, size 4 (S4); and nuts ≥ 25 mm, size 5 (S5). Sizing the sample for each stratum depends on the variance of nut size and on the error level B allowed for either the estimates or the desired precision in the results. The sample size will be larger the greater the variance of the stratum, the lower the error level allowed for the estimates, or the greater the precision desired in the results. For an error B = 0.2 g, the sample...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Anacardium occidentale; Sample size; Sampling precision; Uniform stratified random sampling.
Ano: 2019 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-204X2019000102000
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Sampling of cashew nuts from cashew tree clones. Repositório Alice
ROSSETTI, A. G.; VIDAL NETO, F. das C.; BARROS, L. de M..
Tipo: Artigo de periódico Palavras-chave: Amostragem aleatória estratificada uniforme; Tamanho da amostra; Precisão de amostragem; Sample size; Uniform stratified random sampling; Sampling precision.
Ano: 2020 URL: http://www.alice.cnptia.embrapa.br/alice/handle/doc/1123355
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Sampling plan for using a motorized penetrometer in soil compaction evaluation AGRIAMBI
Storck,Lindolfo; Kobata,Sarha G. K.; Brum,Betania; Soares,André B.; Modolo,Alcir J.; Assmann,Tangriani S..
ABSTRACT This study aimed to estimate the size of blocks of observations of resistance to penetration, obtained by a motorized digital penetrometer, and the number of blocks with semi-amplitude of the confidence interval between 5 and 20% of the mean penetration resistance, for different soil depth ranges and cone diameters. Data were collected in two contrasting plots of a crop-livestock integration experiment, located in Abelardo Luz, SC, Brazil. Ten blocks were delimited and the resistance to penetration was determined in 20 points spaced by 20 cm, using a motorized digital soil penetrometer. To estimate the mean of resistance to penetration, 12 blocks of four points per experimental plot should be used for a semi-amplitude of the confidence interval...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Sample size; Penetration resistance; Grazing pressure; Soil management.
Ano: 2016 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1415-43662016000300250
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Tamanho amostral envolvendo múltiplos caracteres: uma aplicação à digestibilidade em bovinos. Repositório Alice
FREITAS, A. R. de; MANZANO, A.; ESTEVES, S. N..
0 objetivo deste trabalho foi estimar o tamanho amostral mínimo (n) para comparar tratamentos em experimentos de consumo e de digestibilidade com bovinos, envolvendo múltiploscaracteres. Foram utilizados dados de digestibilidade de 72 novilhas com média de 18 meses de idade e 250 kg de peso. 0 experimento foi realizado na Embrapa-Centro de Pesquisa de Pecuária do Sudeste, Sao Carlos, SP, de 1988 a 1989, em delineamento inteiramente casualizado, com nove tratamentos organizados em esquema fatorial 3 x 3 (tres grupos genéticos: Canchim, % Canchim+ % Nelore e Nelore, e tres niveis de proteina bruta: 6, 10 e 13%, com oito repetigbes cada, sendo a unidade ,experimental a novilha). Foram analisados consumo de ragho (g/kg'") por quilograma de peso metabolico,...
Tipo: Artigo de periódico Palavras-chave: Districuicao F; Diferenca minima significativa; Hotelling; Multiplos caracteres; Sample size; F-disstribuition; Minimum significative diference.; Digestibilidade; Gado de Corte.; Digestibility..
Ano: 1999 URL: http://www.alice.cnptia.embrapa.br/alice/handle/doc/44700
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