[R] probit analysis

[Jinsong Zhao]

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