Dear all, I have a very simple set of data and I would like to analyze them with probit analysis.
dose event trial 0.0 3 15 1.1 4 15 1.3 4 15 2.0 3 15 2.2 5 15 2.8 4 15 3.7 5 15 3.9 9 15 4.4 8 15 4.8 11 15 5.9 12 15 6.8 13 15 The dose should be transformed with log10(). I use glm(y ~ log10(dose), family=binomial(link=probit)) to do probit analysis, however, I have to exclude the first observation. In an experimental design, the first observation may be as a control group. I think it should not be simple excluded from the datasets when constructing a model. I refered to SAS online doc for probit procedure, it use the first observation to estimate the natural (threshold) response rate (C). And the final model will be: p = Pr(Y = 0) = C + (1 - C)F(x'\beta) However, I don't know how to considered the control effect when using glm(). Any suggestions will be really appreciated. Best Regards, Jinsong Zhao
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