Robust Calculation of Effective Doses (ED)

This function serves as a robust wrapper for drc::ED. It calculates effective doses (EDs) for multiple specified response levels. Its primary feature is the ability to gracefully handle cases where an ED value is not mathematically estimable from the model (e.g., the requested response is outside the model's asymptotes). Instead of throwing an error, it returns a row of NA values for that specific response level, ensuring the overall analysis can proceed.

Usage

ED_robust(
  mod,
  respLev = c(10, 20, 50),
  interval = get_ed_interval(mod$fct$name, small_n = TRUE),
  CI_level = 0.95,
  verbose = FALSE,
  ...
)

Arguments

mod

An object of class 'drc', representing the fitted dose-response model.

respLev

A numeric vector specifying the response levels for which to calculate ED values (e.g., c(10, 50) for ED10 and ED50).

interval

A character string specifying the method for calculating confidence intervals. Defaults to the output of get_ed_interval(). Common options include "delta", "tfls", or "buckland".

CI_level

A numeric value between 0 and 1 indicating the confidence level for the intervals (e.g., 0.95 for a 95% CI).

verbose

A logical value. If TRUE, the function will print status messages about the calculation progress and any errors encountered for each response level. Default is FALSE.

...

Additional arguments to be passed directly to drc::ED.

Value

A data.table where each row corresponds to a requested response level. The table includes the ED estimate, standard error, confidence interval (Lower, Upper), and metadata about the calculation (confidence level, method, model name, and EC level). Rows for non-estimable EDs are populated with NA.

Author

Hannes Reinwald

Examples

data(lettuce)
m <- drm(weight ~ conc, data = lettuce, fct = BC.4())
ED_robust(m, respLev = c(10, 50), CI_level = 0.95)
#>     Estimate    stderr     Lower    Upper confint_level confint_method
#>        <num>     <num>     <num>    <num>         <num>         <char>
#> 1:  4.457785  1.674585  1.930237 10.29503          0.95           tfls
#> 2: 35.022556 15.426732 13.125303 93.45151          0.95           tfls
#>           model    EC
#>          <char> <num>
#> 1: BC.4:b-d-e-f    10
#> 2: BC.4:b-d-e-f    50