Frequencies for first 10,000 rows of vbac variable in natl2001 dataset :

    Vaginal |
birth after |
   previous |
  C-section |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        129        1.29        1.29
          2 |      9,832       98.32       99.61
          8 |          1        0.01       99.62
          9 |         38        0.38      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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