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

 mri - head |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      9,963       99.63       99.63
        yes |         37        0.37      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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