Frequencies for first 10,000 rows of mammo variable in nhamcsopd2004 dataset :

  mammogram |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      9,775       97.75       97.75
        yes |        225        2.25      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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