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

API codes U |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,996       99.96       99.96
          1 |          4        0.04      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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