Sat, 09/04/2010 - 04:29

Hi,

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_t1 Var_Sib

Var_t2 Var_Sib for one family, then

Var_t1 Var_Sib

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.

Thanks,

Paul

Essentially, the FIML methods assume that data on different rows are independent of each other. Therefore, it is necessary to organize possibly non-independent observations on one line (a wide format). Thus:

Var_t1 Var_t2 Var_Sib1 Var_Sib2

would be an example 'record' or row of the data frame. Note that this means that you need to specify a model with covariance structure capable of describing the largest pedigree, and all smaller ones (which would have missing data coded for non-existent relatives' data).

There is an alternative approach via multilevel modeling, but I don't know of any OpenMx implementation of this for unbalanced pedigrees.

Thanks Mike