Frequencies for first 10,000 rows of ca_downs variable in natl2015 dataset :

       Down |
 Syndrome C |
  Confirmed |      Freq.     Percent        Cum.
------------+-----------------------------------
          C |          2        0.02        0.02
          N |      9,992       99.92       99.94
          P |          5        0.05       99.99
          U |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 20 Oct 2016