gomez.nonnormal1 {agridat} | R Documentation

## 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.

### 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

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

    # Gomez figure 7.3
    ## require(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
    if(require(reshape2) & require(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

[Package agridat version 1.16 Index]