*merge to birth data use "ETBR51FL.DTA", clear sort v001 v002 b16 merge 1:1 v001 v002 b16 using "HW_to_merge.dta" to become this: *merge to birth data use "ETKR51FL.DTA", clear drop if b16==0 | b16==, sort v001 v002 b16 merge 1:1 v001 v002 b16 using "HW_to_merge.dta"