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

Microcephal |
       us U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          1        0.01        0.01
          2 |      9,859       98.59       98.60
          9 |        140        1.40      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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