Frequencies for first 10,000 rows of uca_downs variable in natl2003 dataset :

       Down |
   Syndrome |
        U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          8        0.08        0.08
          2 |      9,038       90.38       90.46
          8 |          6        0.06       90.52
          9 |        948        9.48      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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