In helping us understand how to fit a logistic regression in
R, we are told to first replace 0 and 1 in the response variable by 0.05 and 0.95, respectively and second to take the logit transform of the resulting response variable. Last we fit these data using iterative re-weighted least squares method.
Then we are asked to use 0.005 and 0.995 instead of 0.05 and 0.95. Then the resulting coefficients are quite different.
My question is in
glm function, how are 0 and 1 dealt with? Are they replaced by some numbers as above? What numbers are used by default and why are they used? How sensitive is the choice of these numbers?