Frequencies for first 10,000 rows of xray variable in nhamcsopd1997 dataset :

      x-ray |      Freq.     Percent        Cum.
------------+-----------------------------------
          0 |      9,175       91.75       91.75
          1 |        825        8.25      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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