Frequencies for first 10,000 rows of uld_prepla variable in natl2005 dataset :

   Placenta |
   previa U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         18        0.18        0.18
          2 |      9,863       98.63       98.81
          9 |        119        1.19      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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