Frequencies for first 10,000 rows of ultrasnd variable in nhamcsed2010 dataset :

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
         no |      9,602       96.02       96.02
        yes |        398        3.98      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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