Frequencies for first 10,000 rows of abruptio variable in natl1991 dataset :

   Abruptio |
   placenta |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         42        0.42        0.42
          2 |      9,928       99.28       99.70
          9 |         30        0.30      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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