Frequencies for first 10,000 rows of ultras variable in natlterr1995 dataset :

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      2,878       28.78       28.78
          2 |      7,114       71.14       99.92
          9 |          8        0.08      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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