R help - Apr 2009 - Comparing Proportions Among Groups

Hi everyone,

I am trying to compare proportions among groups using the logistic
regression
approach as follows:

1) Fit the model log(p_i/(1-p_i)) = M + G_i, where p_i is the probability
   of success in group i and G_i is the effect of group i, i=1,..,I.
2) Test the hypotheses:
   Ho: G_1 = G_2 = ... = G_I (the probability of success is the same for all
groups)
   versus
   Ha: at least two G_i's are different (at least two groups have different
probabilities of success)

I am wondering if there any R functions available for accomplishing these
tasks.
Using dummy variables is one option, but is it possible to solve this
problem in R
without resorting to the use of dummy variables?

Many thanks and kind regards,

Isabella

Isabella R. Ghement, Ph.D.
Ghement Statistical Consulting Company
301-7031 Blundell Road, Richmond, B.C., Canada, V6Y 1J5
Tel: 604-767-1250
Fax: 604-270-3922
E-mail: isabella at ghement.ca
Web: www.ghement.ca