Frequencies for first 10,000 rows of vyear variable in nhamcsed1998 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       1997 |        305        3.05        3.05
       1998 |      9,695       96.95      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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