Frequencies for first 10,000 rows of uld_prepla variable in natl2004 dataset :

   Placenta |
   previa U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         27        0.27        0.27
          2 |      8,999       89.99       90.26
          9 |        974        9.74      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 21 Jan 2016