Insecticide treatment effectiveness

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.

Source

Gomez, K.A. and Gomez, A.A.. 1984, Statistical Procedures for Agricultural Research. Wiley-Interscience. Page 300.

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 <!-- %&gt;% 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"))
#> Using trt, rep as id variables


# Gomez table 7.16
m1 <- lm(tlarvae ~ rep + trt, data=dat)
anova(m1)
#> Analysis of Variance Table
#> 
#> 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                      
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
## 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