Frequencies for first 10,000 rows of primac variable in linkco1991us_num dataset :

    Primary |
  C-section |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,172       21.72       21.72
          2 |      7,684       76.84       98.56
          9 |        144        1.44      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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