Frequencies for first 10,000 rows of uca_downs variable in natl2012 dataset :

       Down |
   Syndrome |
        RFP |
771=f_uca_d |
   owns U;R |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          4        0.04        0.04
          2 |      7,553       75.53       75.57
          9 |      2,443       24.43      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 5 May 2016