Frequencies for first 10,000 rows of preplace variable in natl1989 dataset :

   Placenta |
     previa |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         27        0.27        0.27
          2 |      9,748       97.48       97.75
          9 |        225        2.25      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016