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

    Vaginal |
birth after |
   previous |
  C-section |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         94        0.94        0.94
          2 |      9,883       98.83       99.77
          8 |         20        0.20       99.97
          9 |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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