| Year | Value | | 2021 | 2,593 | | 2019 | 6,533 | | 2018 | 6,774 | | 2017 | 7,002 | | 2016 | 7,933 | | 2015 | 7,741 | | 2014 | 8,304 | | 2013 | 9,396 | | 2012 | 8,422.2344798606 | | 2011 | 7,910.2585600468 | | 2010 | 7,681 | | 2009 | 6,142 | | 2008 | 6,105 | | 2007 | 7,366 | | 2006 | 6,905 | | 2005 | 8,181 | | 2004 | 7,885 | | 2003 | 7,214 | | 2002 | 7,304 | | 2001 | 7,138 | | 2000 | 6,703 | | 1999 | 5,900 | | 1998 | 5,400 | | 1997 | 4,900 | | 1996 | 4,200 | | 1995 | 4,000 | | 1994 | 3,600 | | 1993 | 3,800 | | 1992 | 6,300 | | 1991 | 6,700 | | 1990 | 5,800 | | 1989 | 4,900 | | 1988 | 4,600 | | 1987 | 4,300 | | 1986 | 3,300 | | 1985 | 3,500 | | 1984 | 2,800 | | 1983 | 2,600 | | 1982 | 2,600 | | 1981 | 2,600 | | 1980 | 2,700 | | 1979 | 1,600 |
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