Frequencies for first 10,000 rows of f_uca_downs variable in natl2007 dataset :

       Down |
   Syndrome |
(ucs_downs) |
        U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |          1        0.01        0.01
          1 |      9,999       99.99      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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