You can find the values of the quartiles by adding the details option to sum:
sum mpg, d
Now look at the r vector to see where the numbers you want are stored:
return list
You numbers you want are called r(p75) and r(p25). To calculate their difference, type:
gen iqr=r(p75)-r(p25)
You can see the value by typing:
tab iqr
Last Revised: 9/17/2010