Frequencies for first 10,000 rows of prov1990 variable in pos1994 dataset :

        540 |
   antibody |
   detect + |
      other |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      8,798       87.98       87.98
          N |        940        9.40       97.38
          Y |        262        2.62      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 17 May 2017