Frequencies for first 10,000 rows of hivser variable in nhamcsed1999 dataset :

        hiv |
   serology |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,973       99.73       99.73
          1 |         27        0.27      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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