Counts of eelworms before and after fumigant treatments

Format

A data frame with 48 observations on the following 7 variables.

block

block factor, 4 levels

row

row

col

column

fumigant

fumigant factor

dose

dose, Numeric 0,1,2. Maybe should be a factor?

initial

count of eelworms pre-treatment

final

count of eelworms post-treatment

Details

In the original experiment plan (as shown in Bailey 2008), columns 9, 10, 11 are shifted up slightly.

Treatment codes: Con = Control, Chl = Chlorodinitrobenzen, Cym = Cymag, Car = Carbon Disulphide jelly, See = Seekay.

Experiment was conducted in 1935 at Rothamsted Experiment Station. In early March 400 grams of soil were sampled and the number of eelworm cysts were counted. Fumigants were added to the soil, oats were sown and later harvested. In October, the plots were again sampled and the final count of cysts recorded.

Source

Cochran and Cox, 1950. Experimental Designs. Table 3.1.

References

R. A. Bailey, 2008. Design of Comparative Experiments. Cambridge.

Examples

# \dontrun{

library(agridat)
data(cochran.eelworms)
dat <- cochran.eelworms

# Very strong spatial trends
libs(desplot)
desplot(dat, initial ~ col*row,
        flip=TRUE, # aspect unknown
        main="cochran.eelworms")


# final counts are strongly related to initial counts
libs(lattice)
xyplot(final~initial|factor(dose), data=dat, group=fumigant,
       main="cochran.eelworms - by dose (panel) & fumigant",
       xlab="Initial worm count",
       ylab="Final worm count", auto.key=list(columns=5))

# One approach...log transform, use 'initial' as covariate, create 9 treatments
dat <- transform(dat, trt=factor(paste0(fumigant, dose)))
m1 <- aov(log(final) ~ block + trt + log(initial), data=dat)
anova(m1)
#> Analysis of Variance Table
#> 
#> Response: log(final)
#>              Df Sum Sq Mean Sq F value    Pr(>F)    
#> block         3 5.5727  1.8576 23.5588 1.973e-08 ***
#> trt           9 3.4114  0.3790  4.8073  0.000358 ***
#> log(initial)  1 5.2603  5.2603 66.7142 1.582e-09 ***
#> Residuals    34 2.6808  0.0788                      
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

# }