Frequencies for first 10,000 rows of retref variable in nhamcsed2001 dataset :

  return to |
  referring |
  physician |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      8,545       85.45       85.45
          1 |      1,455       14.55      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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