Frequencies for first 10,000 rows of usetobac variable in nhamcsopd2008 dataset :

tobacco use |      Freq.     Percent        Cum.
------------+-----------------------------------
      blank |        422        4.22        4.22
    unknown |      3,169       31.69       35.91
not current |      5,303       53.03       88.94
    current |      1,106       11.06      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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