Frequencies for first 10,000 rows of uop_amnio variable in natl2004 dataset :

Amniocentes |
       is U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        205        2.05        2.05
          2 |      9,135       91.35       93.40
          9 |        660        6.60      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 21 Jan 2016