Frequencies for first 10,000 rows of amnio variable in natl1991 dataset :

Amniocentes |
         is |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        203        2.03        2.03
          2 |      9,785       97.85       99.88
          9 |         12        0.12      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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