Frequencies for first 10,000 rows of prov1910 variable in pos1991 dataset :

        140 |
   virology |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      8,536       85.36       85.36
          N |      1,322       13.22       98.58
          Y |        142        1.42      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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