Re: st: genealogy: how to calculate sibship size

[n j cox <n.j.cox@durham.ac.uk>]

Ronnie Babigumira already directed you to an FAQ explaining various 
tricks. It may be more complicated than you need.

I just wanted to add that if each observation is a person and your 
variables are as stated then the number of people sharing each pair of 
parents is given directly by

bysort ??ther_id : gen n = _N

Thus suppose that our data are

donor_id father_id mother_id
1            A          Z
2            A          Z
3            A          Y
4            A          Y
5            B          Y
6            C          X

then after this

bysort ??ther_id : gen n = _N

you have

donor_id father_id mother_id
1            A          Z             2
2            A          Z             2
3            A          Y             2
4            A          Y             2
5            B          Y             1
6            C          X             1

Note that you don't need a combined id, as you can just
use the two parent ids jointly.

(I enjoyed using the wildcard ??ther_id, as this will catch

father_id mother_id

and (almost certainly) nothing else in your data. If you are
really using French then fortuitously (and fortunately)

??re_id

works the same way.)

Nick
n.j.cox@durham.ac.uk

BAIJER Jan 212040, Ph.D.

I'm trying to have Stata calculate the number of sibs for each of the
families in a list that is composed as follows :

donor_id
father_id
mother_id

From this, I can calculate a unique identifier for the parent couple, by
concatenation of father_id and mother_id.

But, I have no idea how to proceed for this one ...

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