Frequencies for first 10,000 rows of mrihead variable in nhamcsed2008 dataset :

 mri - head |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      9,970       99.70       99.70
        yes |         30        0.30      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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