Frequencies for first 10,000 rows of ultras variable in natl2002 dataset :

 Ultrasound |      Freq.     Percent        Cum.
------------+-----------------------------------
          1 |      5,434       54.34       54.34
          2 |      4,260       42.60       96.94
          9 |        306        3.06      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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