Frequencies for first 10,000 rows of anen variable in linkco1991us_num dataset :

Anencephalu |
          s |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         83        0.83        0.83
          2 |      9,644       96.44       97.27
          9 |        273        2.73      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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