Frequencies for first 10,000 rows of ca_anen variable in natlterr2007 dataset :

Anencephaly |
        RFP |
635=f_ca_an |
       en R |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      6,163       61.63       61.63
          N |      3,833       38.33       99.96
          U |          1        0.01       99.97
          Y |          3        0.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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