Volume of algae as function of increasing concentrations of a herbicide

Dataset from an experiment exploring the effect of increasing concentrations of a herbicide on the volume of the treated algae.

Usage

data(algae)

Format

A data frame with 14 observations on the following 2 variables.

conc: a numeric vector of concentrations.
vol: a numeric vector of response values, that is relative change in volume.

Details

This datasets requires a cubic root transformation in order to stabilise the variance.

Source

Meister, R. and van den Brink, P. (2000) The Analysis of Laboratory Toxicity Experiments, Chapter 4 in Statistics in Ecotoxicology, Editor: T. Sparks, New York: John Wiley & Sons, (pp. 114–116).

Examples

library(drc)
algae.m1 <- drm(vol~conc, data=algae, fct=LL.3())
summary(algae.m1)
#> 
#> Model fitted: Log-logistic (ED50 as parameter) with lower limit at 0 (3 parms)
#> 
#> Parameter estimates:
#> 
#>                Estimate Std. Error t-value   p-value    
#> b:(Intercept)   1.36244    0.16352  8.3321 4.428e-06 ***
#> d:(Intercept) 104.85893    2.57750 40.6825 2.403e-13 ***
#> e:(Intercept)   6.04062    0.69519  8.6892 2.952e-06 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#> 
#> Residual standard error:
#> 
#>  3.911178 (11 degrees of freedom)

algae.m2 <- boxcox(algae.m1)

summary(algae.m2)
#> 
#> Model fitted: Log-logistic (ED50 as parameter) with lower limit at 0 (3 parms)
#> 
#> Parameter estimates:
#> 
#>                Estimate Std. Error t-value   p-value    
#> b:(Intercept)   1.51428    0.10648 14.2207 1.996e-08 ***
#> d:(Intercept) 103.65175    3.96547 26.1386 2.977e-11 ***
#> e:(Intercept)   6.41710    0.73892  8.6845 2.968e-06 ***
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#> 
#> Residual standard error:
#> 
#>  0.7137765 (11 degrees of freedom)
#> 
#> Non-normality/heterogeneity adjustment through Box-Cox transformation
#> 
#> Estimated lambda: 0.5 
#> Confidence interval for lambda: [0.294,0.676] 
#>