Frequencies for first 10,000 rows of amnio variable in natl1994 dataset :

Amniocentes |
         is |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        186        1.86        1.86
          2 |      9,797       97.97       99.83
          9 |         17        0.17      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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