Frequencies for first 10,000 rows of seen72 variable in nhamcsed2007 dataset :

 seen in ed |
    last 72 |
     hours? |      Freq.     Percent        Cum.
------------+-----------------------------------
      blank |        206        2.06        2.06
    unknown |      1,817       18.17       20.23
        yes |        356        3.56       23.79
         no |      7,621       76.21      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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