Frequencies for first 10,000 rows of prov1600 variable in pos1991 dataset :

    patient |
   dialysis |
   training |
       cert |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      9,749       97.49       97.49
          A |        184        1.84       99.33
          B |         64        0.64       99.97
          E |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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