Frequencies for first 10,000 rows of downs variable in natlterr2002 dataset :

     Down's |
   syndrome |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          3        0.03        0.03
          2 |      9,981       99.81       99.84
          8 |         14        0.14       99.98
          9 |          2        0.02      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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