use diar6
reg diarwk mothage motgrd densty pipedwat
ta diarwk
probit diarwk mothage motgrd densty pipedwat
mfx
replace pipedwat=0
predict p0
replace pipedwat=1
predict p1
su p0 p1
clear
use diar6
logit diarwk mothage motgrd densty pipedwat