Frequencies for first 10,000 rows of uld_prepla variable in natlterr2003 dataset :

   Placenta |
   previa U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         24        0.24        0.24
          2 |      9,950       99.50       99.74
          8 |         23        0.23       99.97
          9 |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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