beall.webworms {agridat} | R Documentation |
Counts of webworms in a beet field, with insecticide treatments.
data("beall.webworms")
A data frame with 1300 observations on the following 7 variables.
row
row
col
column
y
count of webworms
block
block
trt
treatment
spray
spray treatment yes/no
lead
lead treatment yes/no
The beet webworm lays egg masses as small as 1 egg, seldom exceeding 5 eggs. The larvae can move freely, but usually mature on the plant on which they hatch.
Each plot contained 25 unit areas, each 1 row by 3 feet long. The row width is 22 inches. The arrangement of plots within the blocks seems certain, but the arrangement of the blocks/treatments is not certain, since the authors say "since the plots were 5 units long and 5 wide it is only practicable to combine them into groups of 5 in one direction or the other".
Treatment 1 = None. Treatment 2 = Contact spray. Treatment 3 = Lead arsenate. Treatment 4 = Both spray, lead arsenate.
Beall, Geoffrey (1940). The fit and significance of contagious distributions when applied to observations on larval insects. Ecology, 21, 460-474. Table 6. http://doi.org/10.2307/1930285
data(beall.webworms) dat <- beall.webworms # Match Beall table 1 with(dat, table(y,trt)) require(lattice) histogram(~y|trt, data=dat, layout=c(1,4), as.table=TRUE, main="beall.webworms") # Visualize Beall table 6. Block effects may exist, but barely. if(require(desplot)){ grays <- colorRampPalette(c("white","#252525")) desplot(y ~ col*row, data=dat, col.regions=grays(10), at=0:10-0.5, out1=block, out2=trt, num=trt, flip=TRUE, # aspect unknown main="beall.webworms (count of worms)") } # Following plot suggests interaction is needed # with(dat, interaction.plot(spray, lead, y)) # Just a simple model here... m1 <- glm(y ~ block+spray*lead, data=dat, family="poisson") summary(m1) anova(m1)