beall.webworms {agridat} | R Documentation

## 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.

### Source

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

### Examples

    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)

[Package agridat version 1.16 Index]