Frequencies for first 10,000 rows of preplace variable in natl1990 dataset :

   Placenta |
     previa |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         26        0.26        0.26
          2 |      9,908       99.08       99.34
          9 |         66        0.66      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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