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Full-Text Articles in Agriculture
Should Blocks Be Fixed Or Random?, Philip Dixon
Should Blocks Be Fixed Or Random?, Philip Dixon
Conference on Applied Statistics in Agriculture
Many studies include some form of blocking in the study design. Block effects are rarely of intrinsic interest; instead they are included in a model so that that model reflects the study design. I consider the question of how these block effects should be modeled: as fixed effects or as random effects. I discuss the consequences of the choice, including the recovery of inter-block information when available, give a simple example to illustrate the connection between recovery of inter-block information and pooling two estimators of a treatment effect, and give an example where fitting a model with random block effects …
Statistical Issues In Next-Generation Sequencing, Paul L. Auer, R. W. Doerge
Statistical Issues In Next-Generation Sequencing, Paul L. Auer, R. W. Doerge
Conference on Applied Statistics in Agriculture
High throughput deep-sequencing or next-generation sequencing has emerged as an exciting new tool in a great number of applications (e.g., variant discovery, profiling of histone modifications, identifying transcription factor binding sites, resequencing, and transcriptome characterization). Even though this technology has generated unprecedented amounts of data in the scientific community few studies have looked carefully at its inherent variability. Recent studies of mRNA expression levels found little appreciable technical variation in Illumina’s Solexa sequencing platform (a next-generation sequencing device). Although these results are encouraging, they are limited to a specific platform and application, and have been made without any attention to …
Statistical Issues In Efficacy Evaluation For Companion Animal Drug Development, Zhanglin Lin Cui, Wherly Hoffman
Statistical Issues In Efficacy Evaluation For Companion Animal Drug Development, Zhanglin Lin Cui, Wherly Hoffman
Conference on Applied Statistics in Agriculture
Companion animals, commonly called pets, are animals such as dogs, cats, and horses. The companion animal drug market has expanded rapidly in recent years. Two major points of focus in companion animal drug development are therapeutics and parasiticides. From a statistics point of view, experimental design, experimental unit determination, sample size estimation and reestimation, treatment design, data transformation, multiple testing, and proper modeling are major statistical issues when efficacy evaluation in a companion animal study is conducted. These major statistical issues are addressed using two clinical studies as examples: Reconcile® (Fluoxetine) for the treatment of separation anxiety in dogs and …
Sample Size Determination In Animal Health Studies, Zhanglin Cui, Alan G. Zimmermann, Daniel H. Mowrey
Sample Size Determination In Animal Health Studies, Zhanglin Cui, Alan G. Zimmermann, Daniel H. Mowrey
Conference on Applied Statistics in Agriculture
Oftentimes in animal health studies, a treatment group is randomly assigned to a pen of animals, and the pen of animals as a whole is treated (fed the same medicated feed or water) together. In this scenario, the pen of animals is the experimental unit and the individual animal may be an observational unit. In addition to having the pen as the experimental unit, if multiple sites are used and site is treated as a random factor, this adds complexity to the study. To properly design the study, it is necessary to determine the number of animals in a pen, …
Modeling And Design To Detect Interaction Of Insecticides, Herbicides And Other Similar Compounds, Timothy E. O'Brien
Modeling And Design To Detect Interaction Of Insecticides, Herbicides And Other Similar Compounds, Timothy E. O'Brien
Conference on Applied Statistics in Agriculture
This paper discusses model and experimental design aspects of agricultural studies aimed at discerning antagonism or synergy between two or more insecticides, herbicides, or other similar compounds. The developed methods involve a broad class of generalised nonlinear models, which are easily fitted to data using popular statistical packages such as the NLMIXED procedure in SAS® software. Sample computer code is given in the Appendix.
Designing Alfalfa Yield Trials For Comparing Long-Term Yields, G. B. Schaalje, S. N. Acharya
Designing Alfalfa Yield Trials For Comparing Long-Term Yields, G. B. Schaalje, S. N. Acharya
Conference on Applied Statistics in Agriculture
An aspect of experimental design that must be taken into consideration for variety trials of perennial crops is the number of years to continue the trial. By tradition, alfalfa forage yield trials are harvested for three or four production years, but the consumers of information from these trials, the producers, often keep their stands in production for more than four years. This study developed a statistical efficiency measure for evaluating the adequacy of forage trial designs with specified numbers of years and replicates, based on a multivariate linear model. The measure was applied to data from four long-term trials grown …
Messy Experimental Designs, Dallas E. Johnson
Messy Experimental Designs, Dallas E. Johnson
Conference on Applied Statistics in Agriculture
This paper describes the statistical analysis of an agricultural experiment that was conducted in a very complex, but somewhat reasonable, experimental design. A correct analysis of data collected from the experimental design used requires the estimation of 8 error terms.