[R] dispersion_parameter_GLMM's

[Cristina Gomes]

Hi all,
I was wondering if somebody could give me advice regarding the 
dispersion parameter in GLMM's. I'm a beginner in R and basically in 
GLMM's. I've ran a GLMM with a poisson family and got really nice 
results that conform with theory, as well with results that I've 
obtained previously with other analysis and that others have obtained in 
similar studies. But the dispersion parameter is too large (25 compared 
to 1). So I ran a quasipoisson that allows for overdispersion and all of 
the significant results fell out. My question is, how much does 
overdispersion invalidate ones results when using a poisson family? What 
could the reason be for having non significant results with a 
quasipoisson distribution?
If anybody could give me some help with this or/and recommend me 
literature that is somewhat comprehensible to lay people (i.e. non 
statisticians) that would be great.
Thanks in advance,
Cristina.