use http://www.ats.ucla.edu/stat/hlm/faq/hsball, clear
sort id
unique  id meanses size sector pracad disclim himinty
preserve
drop size sector pracad disclim himinty meanses
save hsb12_level1

restore
preserve
collapse (mean)  meanses size sector pracad disclim himinty, by(id)
save hsb12_level2
restore