Frequencies for first 10,000 rows of usetobac variable in nhamcsopd2009 dataset :

tobacco use |      Freq.     Percent        Cum.
------------+-----------------------------------
      blank |        573        5.73        5.73
    unknown |      3,594       35.94       41.67
not current |      4,817       48.17       89.84
    current |      1,016       10.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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