Frequencies for first 10,000 rows of sigprov variable in namcs2012 dataset :

 Sigmoidoscopy |
      provided |      Freq.     Percent        Cum.
---------------+-----------------------------------
         Blank |          6        0.06        0.06
Not applicable |      9,976       99.76       99.82
           Yes |         13        0.13       99.95
            No |          5        0.05      100.00
---------------+-----------------------------------
         Total |     10,000      100.00

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