Frequencies for first 10,000 rows of preplace variable in natlterr2001 dataset :

   Placenta |
     previa |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         40        0.40        0.40
          2 |      9,936       99.36       99.76
          8 |         20        0.20       99.96
          9 |          4        0.04      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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