Frequencies for first 10,000 rows of uca_downs variable in natlterr2005 dataset :

       Down |
   Syndrome |
        U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          7        0.07        0.07
          2 |      8,241       82.41       82.48
          9 |      1,752       17.52      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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