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

   Cervical |
   Cerclage |
        RFP |
601=f_ob_ce |
     rvic R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,061       60.61       60.61
          N |      3,916       39.16       99.77
          Y |         23        0.23      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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