Frequencies for first 10,000 rows of ultras variable in natl1999 dataset :

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      7,584       75.84       75.84
          2 |      2,416       24.16      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 22 Dec 2015