Frequencies for first 10,000 rows of forcep variable in natl1991 dataset :

    Forceps |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        981        9.81        9.81
          2 |      9,003       90.03       99.84
          9 |         16        0.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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