Frequencies for first 10,000 rows of uld_prepla variable in natl2003 dataset :

   Placenta |
   previa U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         27        0.27        0.27
          2 |      9,131       91.31       91.58
          8 |          7        0.07       91.65
          9 |        835        8.35      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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