Frequencies for first 10,000 rows of op_cerv variable in natlterr2010 dataset :

   Cervical |
   Cerclage |
        RFP |
601=f_ob_ce |
     rvic R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      4,656       46.56       46.56
          N |      4,301       43.01       89.57
          U |      1,010       10.10       99.67
          Y |         33        0.33      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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