gnm (version 0.8-1)

wheat: Wheat Yields from Mexican Field Trials

Description

Data from a 10-year experiment at the CIMMYT experimental station located in the Yaqui Valley near Ciudad Obregon, Sonora, Mexico --- factorial design using 24 treatments in all. In each of the 10 years the experiment was arranged in a randomized complete block design with three replicates.

Usage

data(wheat)

source

Tables A1 and A3 of Vargas, M, Crossa, J, van Eeuwijk, F, Sayre, K D and Reynolds, M P (2001). Interpreting treatment by environment interaction in agronomy trials. Agronomy Journal 93, 949--960.

Examples

set.seed(1)
data(wheat)

##  Scale yields to reproduce analyses reported in Vargas et al (2001)
yield.scaled <- wheat$yield * sqrt(3/1000)

##  Reproduce (up to error caused by rounding) Table 1 of Vargas et al (2001)
aov(yield.scaled ~ year*tillage*summerCrop*manure*N, data = wheat)
treatment <- interaction(wheat$tillage, wheat$summerCrop, wheat$manure,
                         wheat$N, sep = "")
mainEffects <- lm(yield.scaled ~ year + treatment, data = wheat)
svdStart <- residSVD(mainEffects, year, treatment, 3)
bilinear1 <- update(asGnm(mainEffects), . ~ . + 
                    Mult(year - 1, treatment - 1),
                    start = c(coef(mainEffects), svdStart[,1]))
bilinear2 <- update(asGnm(mainEffects), . ~ . + 
                    Mult(year - 1, treatment - 1, multiplicity = 2),
                    start = c(coef(mainEffects), svdStart[,1:2]))
bilinear3 <- update(asGnm(mainEffects), . ~ . + 
                    Mult(year - 1, treatment - 1, multiplicity = 3),
                    start = c(coef(mainEffects), svdStart[,1:3]))
anova(mainEffects, bilinear1, bilinear2, bilinear3)

##  Examine the extent to which, say, mTF explains the first bilinear term
bilinear1mTF <- gnm(yield.scaled ~ year + treatment + Mult(1 + mTF, treatment),
                    family = gaussian, data = wheat)
anova(mainEffects, bilinear1mTF, bilinear1)