Frequencies for first 10,000 rows of op_ecvs variable in natlterr2006 dataset :

 Successful |
   External |
   Cephalic |
Version RFP |
603=f_ob_su |
       cc R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,275       62.75       62.75
          N |      3,718       37.18       99.93
          Y |          7        0.07      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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