Description Format Details Source References Examples

Wireworms controlled by fumigants in a latin square

A data frame with 25 observations on the following 4 variables.

`row`

row

`col`

column

`trt`

fumigant treatment, 5 levels

`worms`

count of wireworms per plot

Plots were approximately 22 cm by 13 cm. Layout of the experiment was a latin square. The number of wireworms in each plot was counted, following soil fumigation the previous year.

W. G. Cochran (1938).
Some difficulties in the statistical analysis of replicated experiments.
*Empire Journal of Experimental Agriculture*, 6, 157–175.

W. Cochran (1940). The analysis of variance when experimental errors
follow the Poisson or binomial laws.
*The Annals of Mathematical Statistics*, 11, 335-347.

G W Snedecor and W G Cochran, 1980. *Statistical Methods*,
Iowa State University Press. Page 288.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | ```
data(cochran.wireworms)
dat <- cochran.wireworms
if(require(desplot)){
desplot(worms ~ col*row, data=dat,
text=trt, cex=1, # aspect unknown
main="cochran.wireworms")
}
# Trt K is effective, but not the others. Really, this says it all.
require(lattice)
bwplot(worms ~ trt, dat, main="cochran.wireworms", xlab="Treatment")
# Snedecor and Cochran do ANOVA on sqrt(x+1).
dat <- transform(dat, rowf=factor(row), colf=factor(col))
m1 <- aov(sqrt(worms+1) ~ rowf + colf + trt, data=dat)
anova(m1)
# Instead of transforming, use glm
m2 <- glm(worms ~ trt + rowf + colf, data=dat, family="poisson")
anova(m2)
# GLM with random blocking.
if(require(lme4)){
m3 <- glmer(worms ~ -1 +trt +(1|rowf) +(1|colf), data=dat, family="poisson")
summary(m3)
## Fixed effects:
## Estimate Std. Error z value Pr(>|z|)
## trtK 0.1393 0.4275 0.326 0.745
## trtM 1.7814 0.2226 8.002 1.22e-15 ***
## trtN 1.9028 0.2142 8.881 < 2e-16 ***
## trtO 1.7147 0.2275 7.537 4.80e-14 ***
}
``` |

agridat documentation built on May 2, 2019, 4:01 p.m.

Embedding an R snippet on your website

Add the following code to your website.

For more information on customizing the embed code, read Embedding Snippets.