Frequencies for first 10,000 rows of uop_amnio variable in natl2005 dataset :

Amniocentes |
       is U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        200        2.00        2.00
          2 |      9,692       96.92       98.92
          9 |        108        1.08      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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