Frequencies for first 10,000 rows of blank variable in namcs2008 dataset :

      blank |
columns (3) |
 - reserved |
        for |
   possible |
 future use |      Freq.     Percent        Cum.
------------+-----------------------------------
          . |     10,000      100.00      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016