cochran.wireworms {agridat} | R Documentation

## Wireworms controlled by fumigants in a latin square

### Description

Wireworms controlled by fumigants in a latin square

### Format

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

### Details

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.

### Source

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

### References

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.

### Examples

    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 ***

    }

[Package agridat version 1.16 Index]