Hi,

A common problem when studying families is to identify offspring with affected parents. The problem I can't work my mind around is, how to create a new variable and tell Stata to do the lookup.
In this example here, we have only one pedigree, fam_1, where a person with id 9074 is both a mother as well as affected. This is designated by variable is_affected_mom which gets value 1. The pedigree includes a member with id 9307, whose mother person 9074 is, as indicated with the variable mom_id.

How do I tell Stata to check whether mom_id value can be found both in variable id, and at the same time, to get value 1 in variable is_affected_mom?

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str5 family_id    long id long    mom_id    byte is_affected_mom
fam_1    9017    .       .
fam_1    9064    9190    .
fam_1    9074    .       1
fam_1    9232    .       .
fam_1    9233    .       .
fam_1    9234    .       .
fam_1    9235    .       .
fam_1    9307    9074    .
fam_1    9386    9190    .
end
Thank you in advance!

BR Mikko