[R] interpreting interactions in a model

[gaiarrido]

Hi, 
I´ve got this model
> model<-glm(prevalence~agesex+agesex:month,binomial)

and the output of anova is like that

> anova(model,test="Chisq")
                          Df Deviance Resid. Df Resid. Dev P(>|Chi|)   
NULL                            524     206.97             
agesex                 2   9.9165       522     197.05  0.007025 **
agesex:month        9  18.0899       513     178.96  0.034145 *

I don´t know how to interpret the interaction "agesex:month", my mind doubt
between 2 options:
a) For a giving group of "agesex" there are differences between months
b)There are differences between groups of "agesex" in some months but not in
others.

Which option is correct?
Thanks very much

-----
Mario Garrido Escudero
PhD student
Dpto. de Biología Animal, Ecología, Parasitología, Edafología y Qca. Agrícola
Universidad de Salamanca
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