Frequencies for first 10,000 rows of amnio variable in natl1995 dataset :

Amniocentes |
         is |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        182        1.82        1.82
          2 |      9,791       97.91       99.73
          9 |         27        0.27      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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