Frequencies for first 10,000 rows of refer variable in nhamcsopd2000 dataset :

    was pat |
referred by |
        oth |
  physician |
 for visit? |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,291       22.91       22.91
          2 |      5,457       54.57       77.48
          3 |      2,188       21.88       99.36
          4 |         64        0.64      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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