Frequencies for first 10,000 rows of abruptio variable in natl2000 dataset :

   Abruptio |
   placenta |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         53        0.53        0.53
          2 |      9,945       99.45       99.98
          9 |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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