I'm stuck with how one sets up their data frame to take into account relationships beyond that of twins (in my case - sibs and triplets).
For a standard twin model - your data is 'wide' formatted:
ie Var_t1 Var_t2
How do you do this for sibs - the closest I can think is to model a sib against each of their twin siblings, something like:
Var_t2 Var_Sib for one family, then
Var_t2 Var_Sib for another family, etc
and treat the relationship as you do for a DZ pair.
But then I have some twin pairs with multiple sibs - which would become considerably more complex. And also half a dozen triplets. I'm assuming I'm over-complicating things.
I'd appreciate any help.