gen school=0 if grdatn==30
replace school=1 if grdatn==31
replace school=4 if grdatn==32
replace school=6 if grdatn==33
replace school=8 if grdatn==34
replace school=9 if grdatn==35
replace school=10 if grdatn==36
replace school=11 if grdatn==37
replace school=12 if grdatn==38
replace school=12 if grdatn==39
replace school=13 if grdatn==40
replace school=14 if grdatn==41
replace school=14 if grdatn==42
replace school=16 if grdatn==43
replace school=18 if grdatn==44
replace school=20 if grdatn==45
replace school=20 if grdatn==46