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

Microcephal |
         us |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |         16        0.16        0.16
          2 |      9,711       97.11       97.27
          9 |        273        2.73      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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