Frequencies for first 10,000 rows of uca_down variable in linkpe2009psden dataset :

       Down |
   Syndrome |
        U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          4        0.04        0.04
          2 |      9,928       99.28       99.32
          9 |         68        0.68      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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