Frequencies for first 10,000 rows of ctcontrast variable in nhamcsed2014 dataset :

Was CT Scan |
ordered/pro |
 vided with |
intravenous |
       (IV) |
  contrast? |      Freq.     Percent        Cum.
------------+-----------------------------------
      Blank |      8,545       85.45       85.45
    Unknown |        191        1.91       87.36
        Yes |        374        3.74       91.10
         No |        890        8.90      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 11 Apr 2017