Cadmium Daphnia Data

Data from an acute toxicity test exposing Daphnia to cadmium over time. The endpoint measured was mortality (number of dead organisms) at each dose and time point.

Usage

data(CadmiumDaphnia)

Format

A data frame with 58 observations on the following 6 variables.

Dose

a numeric vector of dose values

Time

a numeric vector

Total

a numeric vector

Start

a numeric vector

End

a numeric vector

Dead

a numeric vector

Examples

library(drc)

## Displaying the data
head(CadmiumDaphnia)
#>   Dose Time Total Start End Dead
#> 1  0.0    2    50     0   2    0
#> 2  0.0    4    50     2   4    0
#> 3  0.0    7    50     4   7    0
#> 4  0.0    9    50     7   9    0
#> 5  0.0   11    50     9  11    0
#> 6  0.0   14    50    11  14    0

## Fitting a two-parameter log-logistic model for binomial response at a single time point
CadmiumDaphnia.sub <- CadmiumDaphnia[CadmiumDaphnia$Time == 7, ]
CadmiumDaphnia.m1 <- drm(Dead/Total ~ as.numeric(as.character(Dose)), weights = Total,
data = CadmiumDaphnia.sub, fct = LL.2(), type = "binomial")
summary(CadmiumDaphnia.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:(Intercept)  -1.00362    0.21675 -4.6303 3.651e-06 ***
#> e:(Intercept) 132.42840   51.34644  2.5791  0.009905 ** 
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

## Plotting the fitted curve
plot(CadmiumDaphnia.m1, xlab = "Cadmium dose", ylab = "Proportion dead")