Frequencies for first 10,000 rows of vyear variable in nhamcsed2009 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       2008 |         73        0.73        0.73
       2009 |      9,927       99.27      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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