Frequencies for first 10,000 rows of uop_amnio variable in natlterr2006 dataset :

Amniocentes |
       is U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         13        0.13        0.13
          2 |      4,762       47.62       47.75
          9 |      1,500       15.00       62.75
          . |      3,725       37.25      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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