Frequencies for first 10,000 rows of vyear variable in namcs2001 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       2000 |        129        1.29        1.29
       2001 |      9,871       98.71      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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