Frequencies for first 10,000 rows of f_uca_down variable in linkpe2009psden dataset :

       Down |
 Syndrome U |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |          7        0.07        0.07
          1 |      9,991       99.91       99.98
          . |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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