Frequencies for first 10,000 rows of prov1990 variable in pos1993 dataset :

        540 |
   antibody |
   detect + |
      other |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      8,797       87.97       87.97
          N |        940        9.40       97.37
          Y |        263        2.63      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 26 Jan 2016