Frequencies for first 10,000 rows of ob_ecvf variable in natl2014 dataset :

     Failed |
   External |
   Cephalic |
  Version Y |
        Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,826       98.26       98.26
          U |        142        1.42       99.68
          Y |         32        0.32      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 15 Jun 2016