clear all
set mem 800M
cd data
use observation
sort observeid
save observation, replace
use indmarstatus
keep individid marstatusid mar_sobserveid
rename mar_sobserveid observeid
sort observeid
merge observeid using observation, nokeep keep (obs_de_date)
keep if _merge ==3
global refdate = mdy(12,31,2011)
drop if $refdate < obs_de_date
gen year = year(obs_de_date)
gen period = year($refdate )-year(obs_de_date ) +1
drop obs_de_date
expand period
sort individid year
by individid year: gen p= _n-1
gen rYear = year + p
sort individ rYear 
gen refyear = year($refdate )
sort individid year
egen maxYear = max(year), by(individid rYear)
sort individ rYear
keep if year == maxYear