Frequencies for first 10,000 rows of refer variable in nhamcsopd1999 dataset :

    was pat |
referred by |
        oth |
  physician |
 for visit? |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,120       21.20       21.20
          2 |      5,970       59.70       80.90
          3 |      1,759       17.59       98.49
          4 |        151        1.51      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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