Frequencies for first 10,000 rows of ifyes variable in namcs1993 dataset :

       if seen |
   before, for |
  diagnosis in |
     item 11a? |      Freq.     Percent        Cum.
---------------+-----------------------------------
Not applicable |      1,297       12.97       12.97
           Yes |      6,030       60.30       73.27
            No |      2,673       26.73      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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