In sas and matlab, I have been using a modified link function. I use a binomial distribution with the link log(p-.5/1-p) instead of log(p/1-p) which is the usual logit link. This allows the probabilities to go from .5 to 1 instead of 0 to 1. which is typical when probabilities vary between chance (.5) and certainty (1) in psychophysics experiments. I am trying to access if R can do it. If so could someone show me how to set up the link function so I can call it in the glm function? I know very little about R, the help reads like greek to me, and I can't find an example anywhere. Getting desperate! Anne