Frequencies for first 10,000 rows of ultrasnd variable in nhamcsed2011 dataset :

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
         No |      9,565       95.65       95.65
        Yes |        435        4.35      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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