Frequencies for first 10,000 rows of ultrasnd variable in nhamcsopd2006 dataset :

 ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
         No |      9,515       95.15       95.15
        Yes |        485        4.85      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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