How about collapsing those two levels into one? Wouldn't that work?
Cheers,
Andy
> From: Andrew Criswell
>
> Hello All:
>
> I have a binomial model with one covariate, x1, treated as a
> factor with
> 3 levels. The other covariate is measured x2 <- 1:30. The
> response, y,
> is the proportion of successes out of 20 trials.
>
> glm(cbind(y, 20 - y) ~ x1 * x2, family = binomial)
>
> Now, I would like to constrain the cofficients on 2 levels of the
> factor, x1, to be identical and test the difference between
> these models
> by a likelihood ratio test.
>
> How can I get glm() to constrain the coefficients on 2 levels
> to be the
> same?
>
> Thanks,
> ANDREW
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