Frequencies for first 10,000 rows of contsub6 variable in nhamcsopd1997 dataset :

 controlled |
  substance |
   code for |
 medication |
         #6 |      Freq.     Percent        Cum.
------------+-----------------------------------
          2 |          6        0.06        0.06
          3 |          6        0.06        0.12
          4 |         12        0.12        0.24
          6 |        341        3.41        3.65
          7 |         21        0.21        3.86
          . |      9,614       96.14      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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