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Full-Text Articles in Physical Sciences and Mathematics
Paired Competition Analysis Using Mixed Models, Patrick Gallagher, Bruce A. Craig, Tim Luttermoser, Grzegorz Buczkowski
Paired Competition Analysis Using Mixed Models, Patrick Gallagher, Bruce A. Craig, Tim Luttermoser, Grzegorz Buczkowski
Conference on Applied Statistics in Agriculture
Urban and rural colonies of odorous house ants (Tapinoma sessile) have very different social structures. Urban colonies are very large with hundreds of cohabiting queens, while rural colonies are small with only one queen. To investigate whether worker ant aggressiveness varies across these two colony types, an experiment was performed using an aggression assay, in which 50 ants from each of two colonies were placed in a petri dish and allowed to fight. The response was the total number of dead ants within 24 hours. Because the ants were all the same species and not marked by colony, …
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 …
A Comparison Of Geostatistical And Spatial Autoregressive Approaches For Dealing With Spatially Correlated Residuals In Regression Analysis For Precision Agriculture Applications, Ignacio Colonna, Matías Ruffo, Germán Bollero, Don Bullock
A Comparison Of Geostatistical And Spatial Autoregressive Approaches For Dealing With Spatially Correlated Residuals In Regression Analysis For Precision Agriculture Applications, Ignacio Colonna, Matías Ruffo, Germán Bollero, Don Bullock
Conference on Applied Statistics in Agriculture
Regressions such as Grain yield=f(soil,landscape) are frequently reported in precision agriculture research, and are typically computed using conventional OLS methods, implicitly ignoring spatial correlation of the residuals. This oversight can have a marked effect on the final conclusions derived from these regressions. A further issue is, which approach should be used to account for this problem? We investigated this question using a 2 year data set that includes sitespecific soil and topographic information and soybean yields and compare regression results from direct covariance representation and spatial autoregressive approaches. Our results show that the coefficients from both spatial approaches are in …
Comparing Analyses Of Unbalanced Split-Plot Experiments, Christina D. Smith, Dallas E. Johnson
Comparing Analyses Of Unbalanced Split-Plot Experiments, Christina D. Smith, Dallas E. Johnson
Conference on Applied Statistics in Agriculture
Several procedures for constructing confidence intervals and testing hypotheses about fixed effects in unbalanced split-plot experiments have previously been presented and discussed by Remmenga and Johnson. They recommended a few of the procedures they considered as useful and reliable procedures. Since the advent of the SAS® MIXED procedure, mixed model analyses with REML estimates of the variance components are easily accessible to researchers. This paper compares the analysis of unbalanced split-plot experiments using mixed model procedures with REML estimates of the variance components to the previously established procedures by means of additional simulation studies.
Mixed Models Combined Analysis Of Independent Grazing Trials, H. A. Fribourg, J. C. Waller, R. W. Thompson, W. L. Sanders
Mixed Models Combined Analysis Of Independent Grazing Trials, H. A. Fribourg, J. C. Waller, R. W. Thompson, W. L. Sanders
Conference on Applied Statistics in Agriculture
The mixed models procedure (MMP) was used to analyze pooled data sets from 12 independent studies over 13 yr at 9 locations in 7 states to provide combined estimates of daily gains by beef steers grazing tall fescue pastures with different levels of infestation by Acremonium coenophialum, with and without clover. Spring, summer, and combined spring + summer data were analyzed separately. The MMP permitted estimation of the fixed effects of treatments over a broad inference space of future years and different tall fescue pastures over a wide geographic range, detected some relationships not apparent in the individual studies, …