clear all
set mem 1000M
cd e:\chililabdata\data
use individual
sort individid
replace motherid = trim(motherid)
drop if strlen(motherid) < 11
sort motherid
egen maxchild = count(birthdate), by (motherid)
drop if maxchild < 2
sort motherid birthdate
by motherid: gen no=_n
tostring no, gen(no1)
gen key = motherid + no1
drop no1
sort key
save person1, replace

replace no=no +1
tostring no, gen(no1)
replace key = motherid + no1
keep individid birthdate gender key
rename individid prevchildid
rename birthdate prevbirthdate
rename gender prevgender
sort key
save person2, replace
brow

use person1
merge key using person2
keep if _merge ==3
keep individid  prevchildid prevbirthdate prevgender

sort individid
duplicates drop individid, force
save personRel,  replace
use birth\allbirths

sort individid

merge individid using personRel
keep if _merge!=2
save, replace

cd e:\chililabdata