Frequencies for first 10,000 rows of op_ecvs variable in natlterr2007 dataset :

 Successful |
   External |
   Cephalic |
Version RFP |
603=f_ob_su |
       cc R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,163       61.63       61.63
          N |      3,835       38.35       99.98
          U |          1        0.01       99.99
          Y |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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