Dear S-users,
I am working on a bird where a female either mate with her social
partner, or with other males in the surrounding territories. The
offspring in a nest thus all have the same mother, but can be sired by
one or more males. I divide the offspring into two groups: within-pair
offspring (WPO) or extra-pair offspring (EPO). My data set is arranged
with one female (nest) per row and with data on: number of WPO, number
of EPO and different female traits.
My object is to relate the proportion of extra-pair offspring in a nest
to different traits off the mother. I have defined an EP-offspring as
success, and WP-offspring as failure. I first planned to use an ordinary
glm:
y<-cbind(number of EPO, number of WPO)
glm(y~mother.trait, family=binomial)
However, now I am a unsure whether I need to include 'mother ID' as a
random factor. I.e whether to treat the respons variable (EPO vs WPO per
nest) as a single measure per female. Or should I instead 'imagine' the
response as several measures per female: one measure (EPO or WPO) per
offspring in her nest, and all offspring in her nest having the same
random factor 'mother ID'? If I need a random factor, which glmm do you
suggest?
Thank you for your help!
Sincerely,
Henrik
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Henrik Pärn
Department of Biology
NTNU
7491 Trondheim
Norway
+47 735 96282 (office)
+47 909 89 255 (mobile)
+47 735 96100 (fax)
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