//Building the random selection variable

use nat_combined
gen rand=runiform()
gen select68=1 if rand<=.50 & yr2002==0
gen select02=1 if rand<=.50 & yr2002==1
save nat_combined_select, replace

/*comparing the results of random sample selection to the full data sets*/

histogram age_mom if select68==1, width(1) normal
graph save 3.gph, replace

histogram age_mom if select02==1, width(1) normal
graph save 4.gph, replace

// Now let’s combine graphs from everything we’ve done and see what happens:

clear
cd C:\qm_data
graph combine 1.gph 2.gph 3.gph 4.gph

//FIN