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

    was pat |
referred by |
        oth |
  physician |
 for visit? |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,272       22.72       22.72
          2 |      6,449       64.49       87.21
          3 |      1,176       11.76       98.97
          4 |        103        1.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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