Frequencies for first 10,000 rows of downs variable in natl1991 dataset :

     Down's |
   syndrome |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         31        0.31        0.31
          2 |      9,960       99.60       99.91
          9 |          9        0.09      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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