Frequencies for first 10,000 rows of seen72 variable in nhamcsed2001 dataset :

 seen in ed |
    last 72 |
     hours? |      Freq.     Percent        Cum.
------------+-----------------------------------
      Blank |        332        3.32        3.32
        Yes |        276        2.76        6.08
         No |      8,863       88.63       94.71
    Unknown |        529        5.29      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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