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Registros recuperados: 22
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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 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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Antiretroviral therapy immunologic non-response in a Brazilian population: association study using pharmaco- and immunogenetic markers BJID
Coelho,Antonio V.C.; Moura,Ronald R. de; Guimarães,Rafael L.; Brandão,Lucas A.C.; Crovella,Sergio.
ABSTRACT Background: Antiretroviral therapy (ART) saved millions from HIV-1 infection and AIDS, but some patients do not experience adequate CD4+ T cells gain despite achieving viral suppression. The genetic component of this condition is not yet completely elucidated. Objective: To identify predictive genetic markers of immune response to ART. Methods: Case–control study. Out of 176 HIV-infected patients recruited in the city of Recife, Northeast Brazil, 67 patients with no immunologic response were the cases and the remaining 109 patients who responded were the controls. A set of 94 selected single nucleotide polymorphisms (SNPs) involved in antiretroviral drugs pharmacodynamic pathways and immune system homeostasis were genotyped, while the remaining...
Tipo: Info:eu-repo/semantics/article Palavras-chave: HIV-1; Pharmacodynamics; Immunogenetics; Genetic association study; Survival analysis.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1413-86702018000500392
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Children's Educational Completion Rates and Dropouts in the Context of Ethiopia's National Poverty Reduction Strategy AgEcon
Woldehanna, Tassew; Jones, Nicola; Tefera, Bekele.
A combination of quantitative and qualitative method was used to analyse the determinants of school completion/dropout of children from primary education. A Cox box proportional hazard model was used analyse the survival of children in primary education. The findings have important implications for the formulation and revising Ethiopian Poverty Reduction Strategy Paper. While the policy focus of the 1996-initiated ESDP and the SDPRP (2002-5) on increasing educational access for all has been broadly successful, children from poor and/or highly indebted families still face significant constraints because they have to contribute to household survival through paid and unpaid work. It is therefore imperative to increase efforts to improve the livelihood options...
Tipo: Conference Paper or Presentation Palavras-chave: Education; Children; Ethiopia; PRSP; Poverty; Survival analysis; Labor and Human Capital; A2; D1; J2.
Ano: 2006 URL: http://purl.umn.edu/25351
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Combining Two-Stage Testing and Interval Mapping Strategies to Detect QTL for Resistance to Bonamiosis in the European Flat Oyster Ostrea edulis ArchiMer
Lallias, Delphine; Gomez-raya, L.; Haley, C. S.; Arzul, Isabelle; Heurtebise, Serge; Beaumont, A. R.; Boudry, Pierre; Lapegue, Sylvie.
We have identified quantitative trait loci (QTL) in the flat oyster (Ostrea edulis) for resistance to Bonamia ostreae, a parasite responsible for the dramatic reduction in the aquaculture of this species. An F-2 family from a cross between a wild oyster and an individual from a family selected for resistance to bonamiosis was cultured with wild oysters injected with the parasite, leading to 20% cumulative mortality. Selective genotyping of 92 out of a total of 550 F-2 progeny (i.e., 46 heavily infected oysters that died and 46 parasite-free oysters that survived) was performed using 20 microsatellites and 34 amplification fragment length polymorphism primer pairs. Both a two-stage testing strategy and QTL interval mapping methods were used. The two-stage...
Tipo: Text Palavras-chave: Statistical power; Survival analysis; QTL mapping; Disease resistance; Ostrea edulis.
Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-6682.pdf
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Controlling for time-dependent confounding using marginal structural models AgEcon
Fewell, Zoe; Hernan, Miguel A.; Wolfe, Frederick; Tilling, Kate; Choi, Hyon; Sterne, Jonathan A.C..
Longitudinal studies in which exposures, confounders, and outcomes are measured repeatedly over time have the potential to allow causal inferences about the effects of exposure on outcome. There is particular interest in estimating the causal effects of medical treatments (or other interventions) in circumstances in which a randomized controlled trial is difficult or impossible. However, standard methods for estimating exposure effects in longitudinal studies are biased in the presence of time-dependent confounders affected by prior treatment. This article describes the use of marginal structural models (described by Robins, Hernán, and Brumback [2000]) to estimate exposure or treatment effects in the presence of time-dependent confounders affected by...
Tipo: Journal Article Palavras-chave: Marginal structural models; Causal models; Weighted regression; Survival analysis; Logistic regression; Confounding; Research Methods/ Statistical Methods.
Ano: 2004 URL: http://purl.umn.edu/116267
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Cumulative incidence estimation in the presence of competing risks AgEcon
Coviello, Vincenzo; Boggess, May.
When competing risks are present, the appropriate estimate of the failure probabilities is the cumulative incidence. stcompet creates new variables containing the estimate of this function, its standard error, and ln(−ln) transformed confidence bounds. Two examples are presented to illustrate the use of the new command and some key features of the cumulative incidence.
Tipo: Journal Article Palavras-chave: Stcompet; Survival analysis; Competing risks; Cumulative incidence; Research Methods/ Statistical Methods.
Ano: 2004 URL: http://purl.umn.edu/116230
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Education, tobacco smoking, alcohol consumption, and IL-2 and IL-6 gene polymorphisms in the survival of head and neck cancer BJMBR
López,R.V.M.; Zago,M.A.; Eluf-Neto,J.; Curado,M.P.; Daudt,A.W.; da Silva-Junior,W.A.; Zanette,D.L.; Levi,J.E.; de Carvalho,M.B.; Kowalski,L.P.; Abrahão,M.; de Góis-Filho,J.F.; Boffetta,P.; Wünsch-Filho,V..
The association of education, tobacco smoking, alcohol consumption, and interleukin-2 (IL-2 +114 and -384) and -6 (IL-6 -174) DNA polymorphisms with head and neck squamous cell carcinoma (HNSCC) was investigated in a cohort study of 445 subjects. IL-2 and IL-6 genotypes were determined by real-time PCR. Cox regression was used to estimate hazard ratios (HR) and 95% confidence intervals (95%CI) of disease-specific survival according to anatomical sites of the head and neck. Mean age was 56 years and most patients were males (87.6%). Subjects with 5 or more years of schooling had better survival in larynx cancer. Smoking had no effect on HNSCC survival, but alcohol consumption had a statistically significant effect on larynx cancer. IL-2 gene +114 G/T (HR =...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Smoking; Alcohol; Interleukin; Head and neck cancer; Cancer prognosis; Survival analysis.
Ano: 2011 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2011001000005
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Evaluation of some reproductive traits of Pelibuey ewes under humid tropical conditions of Mexico R. Bras. Zootec.
Luna-Palomera,Carlos; Ojeda-Robertos,Nadia Florencia; Peralta-Torres,Jorge Alonso; Macías-Cruz,Ulises; Sánchez-Dávila,Fernando; Segura-Correa,José Candelario.
ABSTRACT We evaluated the effect of some environmental factors on age at first lambing (AFL) and lambing to conception interval (LCI) of Pelibuey ewes under the humid tropical conditions of Mexico. Ewes grazed on Tanzania (Panicum maximum), Bermuda (Cynodon dactylon), and Brachiaria grass (Brachiaria humidicola) and received hay in the corral in the months of grass scarcity. Reproduction was continuous during the year. Data of 839 lambings from 334 ewes registered from 2009 to 2017 were analyzed using survival analysis procedures. The statistical model for AFL included the effects of year, season, and litter size at lambing, whereas that for LCI included year and season plus parity number of ewe and litter size at weaning. The overall means ± SD for AFL...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Age at first lambing; Lambing to conception interval; Parity number; Tropics; Survival analysis.
Ano: 2019 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-35982019000100600
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G-estimation of causal effects, allowing for time-varying confounding AgEcon
Sterne, Jonathan A.C.; Tilling, Kate.
This article describes the stgest command, which implements G-estimation (as proposed by Robins) to estimate the effect of a time-varying exposure on survival time, allowing for time-varying confounders.
Tipo: Journal Article Palavras-chave: G-estimation; Time-varying confounding; Survival analysis; Research Methods/ Statistical Methods.
Ano: 2002 URL: http://purl.umn.edu/115959
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Graphical representation of interactions AgEcon
Barthel, Friederike Maria-Sophie; Royston, Patrick.
We provide a program to illustrate interactions between treatment and covariates or between two covariates by using forest plots under either the Cox proportional hazards or the logistic regression model. The program is flexible in both the possibility of illustrating more than one interaction at a time and variable specifications of scale.
Tipo: Journal Article Palavras-chave: Fintplot; Interaction; Forest plot; Randomized controlled trial; Survival analysis; Logistic regression; Research Methods/ Statistical Methods.
Ano: 2006 URL: http://purl.umn.edu/117585
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Meniscal allograft transplantation in rabbit Anais da ABC (AABC)
VILELA,LIANA M.; CARLO,RICARDO J. DEL; Melo FILHO,EDSON V.; FAVARATO,LUKIYA S.C.; DUARTE,TATIANA S.; PONTES,KELLY C.S.; CUNHA,DAISE N.Q..
This study evaluated the technique for meniscal allograft transplantation using allografts preserved in glycerin 98% in rabbits. Euthanasia was performed at 70 days to compare the transplanted (TM1 to TM16) versus the contralateral meniscus (OM1 to OM16). Sixteen menisci, 8 transplanted and 8 contralateral, were submitted to gross examination, histomorphometric analysis for identification and quantification of cellular type, and for quantification and distribution of collagen fibers. A revascularization study was conducted in all of the other samples. Lengths of the OM varied from 0.9 to 1.0 cm and two TM were smaller. All TM were completely attached to the synovial membrane, except for one case that presented partial fixation. Both, TM and OM had similar...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Knee; Meniscal allograft; Survival analysis; Transplantation; Revascularization.
Ano: 2015 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652015000502205
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Modelling antagonic effect of lactic acid eacteria supernatants on some pathogenic bacteria BABT
Portella,Augustus Caeser Franke; Karp,Susan; Scheidt,Gessiel Newton; Woiciechwski,Adenise Lorenci; Parada,Jose Luis; Soccol,Carlos Ricardo.
This work presents a statistical model of survival analysis for three pathogenic bacterial strains (Escherichia coli, Listeria monocytogenes and Staphylococcus aureus), when treated with neutralized and non-neutralized filtered supernatants broth from cultures of Lactobacillus acidhophilus, Lactobacillus rhamnosus and Lactobacillus sake. Survival analysis is a method employed to determine the period of time from an initial stage up to the occurrence of a particular event of interest, as death or a particular culture growth failure. In order to evaluate the potential efficacy of the ahead mentioned lactic acid bacteria when used as bioprotective starters in foods, experimental data were statistically treated and expressed by simple representative curves....
Tipo: Info:eu-repo/semantics/article Palavras-chave: Statistical model; Survival analysis; Bioprotection.
Ano: 2009 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132009000700004
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Mortality rate after open Roux-in-Y gastric bypass: a 10-year follow-up BJMBR
Bruschi Kelles,S.M.; Diniz,M.F.H.S.; Machado,C.J.; Barreto,S.M..
The prevalence of obesity has increased to epidemic status worldwide. Thousands of morbidly obese individuals undergo bariatric surgery for sustained weight loss; however, mid- and long-term outcomes of this surgery are still uncertain. Our objective was to estimate the 10-year mortality rate, and determine risk factors associated with death in young morbidly obese adults who underwent bariatric surgery. All patients who underwent open Roux-in-Y gastric bypass surgery between 2001 and 2010, covered by an insurance company, were analyzed to determine possible associations between risk factors present at the time of surgery and deaths related and unrelated to the surgery. Among the 4344 patients included in the study, 79% were female with a median age of...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Survival analysis; Mortality; Follow-up studies; Morbid obesity; Roux-in-Y gastric bypass; Surgeon expertise.
Ano: 2014 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-879X2014000700617
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Nurse effect and herbivory exclusion facilitate plant colonization in abandoned mine tailings storage facilities in north-central Chile RChHN
CUEVAS,JAIME G; SILVA,SERGIO I; LEÓN-LOBOS,PEDRO; GINOCCHIO,ROSANNA.
Positive interactions among plants, such as the nurse effect, can attenuate environmental stress (e.g., drought) or reduce the intensity of perturbations (e.g., herbivory), thus enhancing the possibility of regeneration in natural systems. This study analyses the potential use of nurse plants for restoring artificial environments, such as mine hard-rock dumps. We evaluated seedling recruitment and survival in open areas and beneath the canopy of nurse shrubs, with and without grazing exclusion, on an abandoned copper tailings storage facility in north-central Chile. The nurse species was Baccharis linearis (Asteraceae), and seedling species were B. linearis, Haplopappus parvifolius (Asteraceae), Schismus arabicus (Poaceae), and several forb/grass taxa. A...
Tipo: Journal article Palavras-chave: Baccharis linearis; Haplopappus parvifolius; Hard rock waste; Primary succession; Survival analysis.
Ano: 2013 URL: http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0716-078X2013000100006
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Phenotypic relationships between type traits and productive life using a piecewise Weibull proportional hazard model Scientia Agricola
Kern,Elisandra Lurdes; Cobuci,Jaime Araujo; Costa,Cláudio Napolis; Ducrocq,Vincent.
ABSTRACT: Longevity is an important trait due to its relationship with profitability. Type traits have been used as indirect predictors for productive life. The objective of this study was to evaluate the relationship of 20 type traits on length of productive life in Brazilian Holsteins, using a piecewise Weibull proportional hazard model. Three analyses were performed i) productive life was corrected for within herd level of production as a proxy for functional longevity, which included the time-dependent effects of region within year, class of milk production within herdyear, milk production class within lactation number, fat class and protein contents within herd and (variation in) herd size as well as the time-independent fixed effect of age at first...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Conformation traits; Dairy cattle; Longevity; Culling risk; Survival analysis.
Ano: 2018 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-90162018000600470
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Product Life Cycles and Innovation in the US Seed Corn Industry AgEcon
Magnier, Alexandre; Kalaitzandonakes, Nicholas G.; Miller, Douglas J..
The purpose of this study is to evaluate potential changes in the length of product life cycles in the US seed corn industry. We use the observed survival time on the market for hybrids sold during 1997-2009 to conduct a survival analysis. Our empirical results show that the expected lifetimes for corn hybrids with single biotech traits are 5-15% longer than for hybrids with multiple (stacked) traits, and the expected lifetimes for conventional corn are 13-17% longer than stacked hybrids. Also, the product life cycles for all types of hybrids have decreased over the past twelve years (especially after 2004), but the rate of decline is roughly similar across hybrid types. Based on this evidence, we conclude that the shorter product life cycles are closely...
Tipo: Journal Article Palavras-chave: Accelerated failure time; Biotechnology; Product life cycle; Survival analysis; Productivity Analysis; Research and Development/Tech Change/Emerging Technologies; Research Methods/ Statistical Methods; Risk and Uncertainty.
Ano: 2010 URL: http://purl.umn.edu/93557
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Programmable GLM: Two user-defined links AgEcon
Guan, Weihua; Gutierrez, Roberto G..
With the release of Stata 7, the glm command for fitting generalized linear models underwent a substantial overhaul. Stata 7 glm contains an expanded array of variance estimators, regression diagnostics, and other enhancements. The overhaul took place to coincide with the release of Hardin and Hilbe (2001). With the new glm came a modular design that enables users to program customized link functions, variance functions, and weight functions to be used if Newey-West covariance estimates are desired. Because cases requiring customized link functions are the more prevalent in the literature, only those are considered here. We give two examples where a nonstandard link function is required: the relative survival model of Hakulinen and Tenkanen (1987) and a...
Tipo: Journal Article Palavras-chave: GLM; Survival analysis; Cox regression; Programming; Research Methods/ Statistical Methods.
Ano: 2002 URL: http://purl.umn.edu/116023
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Reproduction and survival of Muscina stabulans under laboratory conditions Ciência Rural
Krüger,Rodrigo Ferreira; Ribeiro,Paulo Bretanha; Erthal,Simone Giehl; DeSouza,Og.
This is the first published report concerning reproduction and survival using life table analyses of fertility and survival for Muscina stabulans maintained under laboratory conditions with artificial diets. The intrinsic rate of growth, reproduction rate and average generational time were obtained, suggesting a rapid population growth under these rearing conditions. These findings permitted the creation of time models of survival and oviposition, as well as a quantitative estimate of the adaptation capacity of this species.
Tipo: Info:eu-repo/semantics/article Palavras-chave: Life table; Survival analysis; Population growth.
Ano: 2010 URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-84782010000300030
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Review of Regression Methods in Biostatistics: Linear, Logistic, Survival, and Repeated Measures Models by Vittinghoff, Glidden, Shiboski, and McCulloch AgEcon
Lemeshow, Stanley; Moeschberger, Melvin L..
This article reviews Regression Methods in Biostatistics: Linear, Logistic, Survival, and Repeated Measures Models by Vittinghoff et al.
Tipo: Journal Article Palavras-chave: Linear regression; Logistic regression; Survival analysis; Repeated measures; Generalized linear models; Complex surveys; Research Methods/ Statistical Methods.
Ano: 2005 URL: http://purl.umn.edu/117518
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