Frequencies for first 10,000 rows of op_ecvs variable in natlterr2008 dataset :

 Successful |
   External |
   Cephalic |
Version RFP |
603=f_ob_su |
       cc R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,061       60.61       60.61
          N |      3,926       39.26       99.87
          Y |         13        0.13      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 May 2016