| Year | Value | | 2021 | 2,478 | | 2020 | 1,918 | | 2019 | 1,967 | | 2018 | 2,244 | | 2017 | 2,218 | | 2009 | 3,480 | | 2008 | 3,510 | | 2007 | 3,508 | | 2006 | 3,573 | | 2005 | 3,083 | | 2004 | 3,683 | | 2003 | 3,911 | | 2002 | 3,876 | | 2001 | 2,744 | | 2000 | 2,324 | | 1999 | 3,700 | | 1998 | 3,600 | | 1997 | 3,900 | | 1996 | 4,600 | | 1995 | 8,300 | | 1994 | 8,800 | | 1993 | 5,500 | | 1992 | 5,500 | | 1991 | 3,300 | | 1990 | 3,300 | | 1989 | 2,800 | | 1988 | 2,600 | | 1987 | 2,500 |
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