Frequencies for first 10,000 rows of amnio variable in natl1989 dataset :

Amniocentes |
         is |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        237        2.37        2.37
          2 |      9,709       97.09       99.46
          9 |         54        0.54      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 3 Jan 2016