Frequencies for first 10,000 rows of f_uop_ultra variable in linkpe2009psden dataset :

 Ultrasound |
          U |      Freq.     Percent        Cum.
------------+-----------------------------------
          . |     10,000      100.00      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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