Frequencies for first 10,000 rows of refered variable in nhamcsopd2007 dataset :

   refer to |
  emergency |
 department |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      9,971       99.71       99.71
        yes |         29        0.29      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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