Frequencies for first 10,000 rows of vyear variable in namcs1997 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       1996 |         58        0.58        0.58
       1997 |      9,942       99.42      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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