Frequencies for first 10,000 rows of vyear variable in nhamcsopd1999 dataset :

    year of |
      visit |      Freq.     Percent        Cum.
------------+-----------------------------------
       1998 |        308        3.08        3.08
       1999 |      9,692       96.92      100.00
------------+-----------------------------------
      Total |     10,000      100.00

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