Frequencies for first 10,000 rows of preplace variable in natl1992 dataset :

   Placenta |
     previa |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         22        0.22        0.22
          2 |      9,942       99.42       99.64
          9 |         36        0.36      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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