Four-parameter Brain-Cousens hormesis model

BC.4 provides the Brain-Cousens modified log-logistic model with the lower limit fixed at 0.

Usage

BC.4(fixed = c(NA, NA, NA, NA), names = c("b", "d", "e", "f"), ...)

Arguments

fixed: numeric vector of length 4 specifying fixed parameters (NAs for free parameters).
names: a vector of character strings giving the names of the parameters.
...: additional arguments passed to braincousens.

Value

A list (see braincousens).

References

van Ewijk, P. H. and Hoekstra, J. A. (1993) Calculation of the EC50 and its Confidence Interval When Subtoxic Stimulus Is Present, Ecotoxicology and Environmental Safety, 25, 25–32.

Author

Christian Ritz

Examples

lettuce.bcm2 <- drm(weight ~ conc, data = lettuce, fct = BC.4())
summary(lettuce.bcm2)
#> 
#> Model fitted: Brain-Cousens (hormesis) with lower limit fixed at 0 (4 parms)
#> 
#> Parameter estimates:
#> 
#>               Estimate Std. Error t-value   p-value    
#> b:(Intercept) 1.282812   0.049346 25.9964 1.632e-10 ***
#> d:(Intercept) 0.967302   0.077123 12.5423 1.926e-07 ***
#> e:(Intercept) 0.847633   0.436093  1.9437   0.08059 .  
#> f:(Intercept) 1.620703   0.979711  1.6543   0.12908    
#> ---
#> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
#> 
#> Residual standard error:
#> 
#>  0.1117922 (10 degrees of freedom)
ED(lettuce.bcm2, c(50))
#> 
#> Estimated effective doses
#> 
#>      Estimate Std. Error
#> e:50   35.023     15.427