Frequencies for first 10,000 rows of uop_amnio variable in natl2006 dataset :

Amniocentes |
       is U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        189        1.89        1.89
          2 |      9,677       96.77       98.66
          9 |        134        1.34      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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