Frequencies for first 10,000 rows of op_cerv variable in natlterr2011 dataset :

   Cervical |
   Cerclage |
        RFP |
601=f_ob_ce |
     rvic R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      2,536       25.36       25.36
          N |      6,300       63.00       88.36
          U |      1,142       11.42       99.78
          Y |         22        0.22      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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