Frequencies for first 10,000 rows of seen72 variable in nhamcsed2006 dataset :

 seen in ed |
    last 72 |
     hours? |      Freq.     Percent        Cum.
------------+-----------------------------------
      blank |        122        1.22        1.22
        yes |        386        3.86        5.08
         no |      8,489       84.89       89.97
    unknown |      1,003       10.03      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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