Frequencies for first 10,000 rows of smokcig variable in nhamcsed1996 dataset :

       does |
    patient |
      smoke |
cigarettes? |      Freq.     Percent        Cum.
------------+-----------------------------------
        Yes |        655        6.55        6.55
         No |      3,177       31.77       38.32
    Unknown |      6,168       61.68      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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