Frequencies for first 10,000 rows of uop_ultra variable in natlterr2005 dataset :

 Ultrasound |
          U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |        878        8.78        8.78
          2 |      3,594       35.94       44.72
          9 |      1,783       17.83       62.55
          . |      3,745       37.45      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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