Frequencies for first 10,000 rows of ca_anen variable in natl2013 dataset :

Anencephaly |
        RFP |
635=f_ca_an |
       en R |      Freq.     Percent        Cum.
------------+-----------------------------------
          N |      9,997       99.97       99.97
          Y |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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