Frequencies for first 10,000 rows of vyear variable in namcs2008 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       2007 |         29        0.29        0.29
       2008 |      9,971       99.71      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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