agridat (version 1.23)

gomez.nonnormal1: Insecticide treatment effectiveness

Description

Insecticide treatment effectiveness

Usage

data("gomez.nonnormal1")

Format

A data frame with 36 observations on the following 3 variables.

trt

insecticidal treatment

rep

replicate

larvae

number of larvae

Details

Nine treatments (including the control, T9) were used on four replicates. The number of living insect larvae were recorded.

The data show signs of non-normality, and a log transform was used by Gomez.

Used with permission of Kwanchai Gomez.

References

None.

Examples

library(agridat)
data(gomez.nonnormal1)
dat <- gomez.nonnormal1

# Gomez figure 7.3
## libs(dplyr)
## dat2 <- dat %>% group_by(trt)
## dat2 <- summarize(dat2, mn=mean(larvae), rng=diff(range(larvae)))
## plot(rng ~ mn, data=dat2,
##      xlab="mean number of larvae", ylab="range of number of larvae",
##      main="gomez.nonnormal1")


# Because some of the original values are less than 10,
# the transform used is log10(x+1) instead of log10(x).
dat <- transform(dat, tlarvae=log10(larvae+1))

# QQ plots for raw/transformed data
libs(reshape2, lattice)
qqmath( ~ value|variable, data=melt(dat),
       main="gomez.nonnormal1 - raw/transformed QQ plot",
       scales=list(relation="free"))


# Gomez table 7.16
m1 <- lm(tlarvae ~ rep + trt, data=dat)
anova(m1)
## Response: tlarvae
##           Df Sum Sq Mean Sq F value    Pr(>F)
## rep        3 0.9567 0.31889  3.6511 0.0267223 *
## trt        8 3.9823 0.49779  5.6995 0.0004092 ***
## Residuals 24 2.0961 0.08734