Hi all,

I am trying to do a generalized estimating equation (GEE) with the "geepack"
package and I am not 100% sure what exactly the "id" argument means. It
seems to be an important argument because results differ considerably
defining different clusters.

I have a data set of counts (poisson distribution): numbers of butterfly
species counted every month during a period of one year (12 repeated
measures) at seven sites, three of those being "continuous forest sites" and
four of those being "secondary forest sites". The aim is to compare
continuous and secondary forests.

Would you define the sites or the forest type as id argument:

model1<-geeglm(formula = number ~ type + month, family = poisson, *id = site
*, corstr = "ar1")

model2<-geeglm(formula = number ~ type + month, family = poisson, *id = type
*, corstr = "ar1")

or should even almost every count have a special id (e.g. *
id=interaction(month,site)* or *id=interaction(month,type*))

Thanks for your help...
Anna

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