Frequencies for first 10,000 rows of vyear variable in namcs2009 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       2008 |        100        1.00        1.00
       2009 |      9,900       99.00      100.00
------------+-----------------------------------
      Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016