Frequencies for first 10,000 rows of refer variable in nhamcsopd1998 dataset :

    was pat |
referred by |
        oth |
  physician |
 for visit? |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,213       22.13       22.13
          2 |      6,798       67.98       90.11
          3 |        860        8.60       98.71
          4 |        129        1.29      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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