Frequencies for first 10,000 rows of ifyes variable in nhamcsopd1992 dataset :

       If seen |
   before, for |
  diagnosis in |
     item 11a? |      Freq.     Percent        Cum.
---------------+-----------------------------------
Not applicable |      2,194       21.94       21.94
           Yes |      6,192       61.92       83.86
            No |      1,614       16.14      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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