Frequencies for first 10,000 rows of preplace variable in natlterr1998 dataset :

   Placenta |
     previa |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         33        0.33        0.33
          2 |      9,963       99.63       99.96
          9 |          4        0.04      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Dec 2015