Frequencies for first 10,000 rows of uop_amnio variable in natl2003 dataset :

Amniocentes |
       is U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        208        2.08        2.08
          2 |      9,024       90.24       92.32
          8 |          7        0.07       92.39
          9 |        761        7.61      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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