agridat (version 1.16)

beall.webworms: Counts of webworms in a beet field, with insecticide treatments.

Description

Counts of webworms in a beet field, with insecticide treatments.

Usage

data("beall.webworms")

Format

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

Details

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.

Examples

# NOT RUN {
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)

# }