Frequencies for year variable in ambulatory_surgical_measures_state dataset :

       Year |      Freq.     Percent        Cum.
------------+-----------------------------------
       2013 |         53       50.00       50.00
       2014 |         53       50.00      100.00
------------+-----------------------------------
      Total |        106      100.00

by Jean Roth , jroth@nber.org , 15 Nov 2016