Frequencies for first 10,000 rows of seen72 variable in nhamcsed2002 dataset :

 seen in ed |
    last 72 |
     hours? |      Freq.     Percent        Cum.
------------+-----------------------------------
      Blank |        235        2.35        2.35
        Yes |        225        2.25        4.60
         No |      8,855       88.55       93.15
    Unknown |        685        6.85      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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