Frequencies for first 10,000 rows of uca_downs variable in natl2005 dataset :

       Down |
   Syndrome |
        U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          2        0.02        0.02
          2 |      9,858       98.58       98.60
          9 |        140        1.40      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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