Frequencies for first 10,000 rows of uop_ultra variable in natl2006 dataset :

 Ultrasound |
          U |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      4,906       49.06       49.06
          2 |      4,960       49.60       98.66
          9 |        134        1.34      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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