For many non-linear functions it may be possible to obtain sensible initial parameter values using the interpretation of the parameters. For the fo...

For many non-linear functions it may be possible to obtain sensible initial parameter values using the interpretation of the parameters. For the four-parameter logistic function this is done by using the maximum (initial value of d) and minimum (initial value of c) value of the ys and then making the transformation 4 Bioassay Analysis using R log (d− y y − c ) = b(log(x)− log(e)). (5) Now linear regression can be used to obtain initial values of b and e. The procedure described can be captured in a function which for a given data set returns starting values. We will refer to such a function as a self starter function..