Frequencies for first 10,000 rows of op_tocol variable in natl2013 dataset :

  Tocolysis |
        RFP |
602=f_ob_to |
       co R |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,729       97.29       97.29
          U |        213        2.13       99.42
          Y |         58        0.58      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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