probit etc. for dose-response modeling

Hello all

I have done some fitting of pnorm functions to dose-response data, so I could
calculate EC50 values (dose where the response is 0.5). I used the nlm function
for this, so I did not get any information about the confidence intervals of
the fitted parameters.

What would be a good way to do such a probit fit, or is there a package which I
could use?

Best regards

Johannes Ranke
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