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

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
         No |      9,559       95.59       95.59
        Yes |        441        4.41      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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