drda 2.0.0

It is now possible to fit models using either the log-dose or the dose scale.

To accommodate this extension it was necessary to change the default model parameterization, which now follows that of the Emax model (Macdougall, 2006).

Briefly, the 5-parameter logistic function is now defined as

alpha + delta / (1 + nu * exp(-eta * (x - phi)))^(1 / nu)

Parameter alpha is the value of the function when x approaches -Inf. Parameter delta is the (signed) height of the curve. Parameter eta > 0 represents the steepness (growth rate) of the curve. Parameter phi is related to the mid-value of the function. Parameter nu affects near which asymptote maximum growth occurs.

Similarly, the newly implemented log-logistic function (when x >= 0) is defined as

alpha + delta * (x^eta / (x^eta + nu * phi^eta))^(1 / nu)

Check the vignette (vignette("drda", package = "drda")) or the help page (help(drda)) to know more about the available models.

Here is a change log from previous version:

• Change parameterization to follow that of the Emax model.
• Implement the log-logistic family of models.
• Improve initialization algorithm to be more efficient and (hopefully) robust.
• Exported functions for evaluating theoretical gradient and Hessian of each implemented model.
• Implement the effective_dose function for estimating effective doses.
• Added examples to help pages.
• Many minor bug fixes (too many to list them all).

drda 1.0.0

First public release.