Frequencies for first 10,000 rows of usetobac variable in nhamcsopd2010 dataset :

tobacco use |      Freq.     Percent        Cum.
------------+-----------------------------------
      blank |        322        3.22        3.22
    unknown |      3,015       30.15       33.37
not current |      5,467       54.67       88.04
    current |      1,196       11.96      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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