Frequencies for first 10,000 rows of refer variable in nhamcsopd1993 dataset :

    was pat |
   referred |
  for visit |
 by another |
 physician? |      Freq.     Percent        Cum.
------------+-----------------------------------
        Yes |      2,107       21.07       21.07
         No |      7,893       78.93      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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