guthion

Data from an acute toxicity test with the insecticide guthion (azinphos-methyl). For each dose level in two treatment groups, the numbers of alive, moribund, and dead subjects were recorded.

Usage

data(guthion)

Format

A data frame with 6 observations on the following 6 variables.

trt

a categorial vector

dose

a numeric vector

alive

a numeric vector

moribund

a numeric vector

dead

a numeric vector

total

a numeric vector

Examples

library(drc)

## Displaying the data
head(guthion)
#>   trt dose alive moribund dead total
#> 1   S 20.0    44        1    5    50
#> 2   S 35.0    28        1   21    50
#> 3   S 45.0     8        7   35    50
#> 4   T  1.0    37        1   12    50
#> 5   T  1.5    20        2   28    50
#> 6   T  2.0     8        6   36    50

## Fitting a two-parameter log-logistic model for binomial response
guthion.m1 <- drm(dead/total ~ dose, trt, weights = total,
data = guthion, fct = LL.2(), type = "binomial")
summary(guthion.m1)
#> 
#> Model fitted: Log-logistic (ED50 as parameter) with lower limit at 0 and upper limit at 1 (2 parms)
#> 
#> Parameter estimates:
#> 
#>      Estimate Std. Error t-value   p-value    
#> b:S -3.768548   0.712361 -5.2902 1.222e-07 ***
#> b:T -3.051117   0.656853 -4.6451 3.400e-06 ***
#> e:S 36.891558   1.887823 19.5418 < 2.2e-16 ***
#> e:T  1.432554   0.083677 17.1201 < 2.2e-16 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

## Plotting the fitted curves
plot(guthion.m1, xlab = "Dose", ylab = "Proportion dead", ylim = c(0, 1))