Frequencies for first 10,000 rows of hivser variable in nhamcsed1997 dataset :

        hiv |
   serology |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,981       99.81       99.81
          1 |         19        0.19      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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