[R] poisson regression nested effects

[Katalin Csillery]

Dear All,

I have two treatment levels and multinomial behaviors as response
and also a covariate (size). The individuals were split to the two
treatment levels on the first day and switched on the second day. 
I am interested not only the treatmen effect but the effect of the day,
such that the individuals experinced treatment 1 first, or treatment 2
first.

I conditioned on the most frequent behavior and than run separate poisson
models on the rest of the behaviors (proportions of time when they did a 
behavior given that they do not do the most frequent).

glm(behav1~treatment*day+size, family=poisson(), data=data)

I wonder that it is not correct because the day effect is nested in the
treatment effect but I do not know how set it up in glm().

Also do I need to do any corrections because of the separate tests on
each beahvior? It is more a statistical question.

Thanks for any help in advance!

Katalin