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

   Cervical |
   Cerclage |
        RFP |
601=f_ob_ce |
     rvic R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,163       61.63       61.63
          N |      3,812       38.12       99.75
          U |          1        0.01       99.76
          Y |         24        0.24      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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