Frequencies for first 10,000 rows of hivser variable in nhamcsed2003 dataset :

        hiv |
   serology |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      9,980       99.80       99.80
        yes |         20        0.20      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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