Frequencies for first 10,000 rows of amnio variable in natlterr2000 dataset :

Amniocentes |
         is |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        145        1.45        1.45
          2 |      9,849       98.49       99.94
          9 |          6        0.06      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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