use observation
sort observeid
save observation, replace
use medinsurance
keep individid hinsid hin_sobserveid
rename hin_sobserveid observeid
sort observeid
merge observeid using observation, nokeep keep (obs_de_date)
gen refdate = $refdate  + 180
drop if refdate < obs_de_date
gen period = qofd(refdate )-qofd(obs_de_date ) +1
expand period
sort individid obs_de_date
by individid obs_de_date: gen p= _n-1
gen quarterdate = qofd(obs_de_date) + p
gen refquarter = qofd(refdate )
sort individid quarterdate
egen maxobs_de_date = max(obs_de_date), by(individid quarterdate)
keep if obs_de_date == maxobs_de_date 
sort individid
tostring quarterdate, generate(key)
replace key = individid + key
duplicates drop key, force
drop _merge
sort key
save crossmedinsurancetemp, replace
keep if refquarter == quarterdate 
format refdate %td
keep individid hinsid refdate obs_de_date observeid
duplicates drop individid, force
sort individid
save cross\crossmedinsurance, replace