Frequencies for first 10,000 rows of ca_anen variable in natlterr2015 dataset :

Anencephaly |
      Y Yes |      Freq.     Percent        Cum.
------------+-----------------------------------
            |      1,078       10.78       10.78
          N |      8,807       88.07       98.85
          U |        114        1.14       99.99
          Y |          1        0.01      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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