Frequencies for first 10,000 rows of uop_amnio variable in natlterr2003 dataset :

Amniocentes |
       is U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        130        1.30        1.30
          2 |      9,847       98.47       99.77
          8 |         23        0.23      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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