Frequencies for first 10,000 rows of rupture variable in natlterr2001 dataset :

  Premature |
 rupture of |
   membrane |
(>12 hours) |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        203        2.03        2.03
          2 |      9,773       97.73       99.76
          8 |         20        0.20       99.96
          9 |          4        0.04      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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