Frequencies for first 10,000 rows of retreffu variable in nhamcsed2007 dataset :

return/refe |
       r to |
physician/c |
  linic for |
         fu |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      3,545       35.45       35.45
        yes |      6,455       64.55      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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