Frequencies for first 10,000 rows of tocol variable in natl1990 dataset :

  Tocolysis |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         67        0.67        0.67
          2 |      9,889       98.89       99.56
          9 |         44        0.44      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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