Frequencies for first 10,000 rows of preplace variable in natl1999 dataset :

   Placenta |
     previa |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         28        0.28        0.28
          2 |      9,972       99.72      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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