Frequencies for first 10,000 rows of op_cerv variable in natlterr2012 dataset :

   Cervical |
   Cerclage |
        RFP |
601=f_ob_ce |
     rvic R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      1,163       11.63       11.63
          N |      8,403       84.03       95.66
          U |        404        4.04       99.70
          Y |         30        0.30      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 5 May 2016