Frequencies for first 10,000 rows of retreffu variable in nhamcsed2009 dataset :

return/refe |
       r to |
physician/c |
  linic for |
         fu |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      3,753       37.53       37.53
          1 |      6,247       62.47      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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