Frequencies for first 10,000 rows of contsub6 variable in nhamcsopd1996 dataset :

 controlled |
  substance |
   code for |
 medication |
         #6 |      Freq.     Percent        Cum.
------------+-----------------------------------
          2 |          3        0.03        0.03
          3 |          6        0.06        0.09
          4 |         16        0.16        0.25
          6 |        433        4.33        4.58
          7 |         21        0.21        4.79
          . |      9,521       95.21      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016