Frequencies for first 10,000 rows of microce variable in natl1998 dataset :

Microcephal |
         us |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |          1        0.01        0.01
          2 |      9,983       99.83       99.84
          9 |         16        0.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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