Frequencies for first 10,000 rows of ultras variable in natlterr1997 dataset :

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      3,505       35.05       35.05
          2 |      6,495       64.95      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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