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).

First public release.