Frequencies for first 10,000 rows of comstat2 variable in nhamcsopd2011 dataset :

Composition status |
          code for |
     Medication #2 |      Freq.     Percent        Cum.
-------------------+-----------------------------------
Single entity drug |      4,442       44.42       44.42
  Combination drug |        467        4.67       49.09
      Undetermined |         71        0.71       49.80
                 . |      5,020       50.20      100.00
-------------------+-----------------------------------
             Total |     10,000      100.00

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