Frequencies for first 10,000 rows of amnio variable in natl1999 dataset :

Amniocentes |
         is |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        124        1.24        1.24
          2 |      9,876       98.76      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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