Frequencies for first 10,000 rows of f_uca_hydro variable in natl2005 dataset :

Hydrocephal |
       us U |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |         13        0.13        0.13
          1 |      9,987       99.87      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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