| Year | Value | | 2021 | 2.0710266375726 | | 2020 | -4.7255905906475 | | 2019 | 0.87008367326702 | | 2018 | 1.3567061091026 | | 2017 | 2.2314561358909 | | 2016 | 3.2239939329896 | | 2015 | 2.7594968390817 | | 2014 | 2.5402533553525 | | 2013 | 0.55827655557688 | | 2012 | 0.17541465656703 | | 2011 | 3.9017094524111 | | 2010 | 3.7154894493617 | | 2009 | -4.2335558183023 | | 2008 | 0.85249218938111 | | 2007 | 2.8163746799956 | | 2006 | 4.6267473995627 | | 2005 | 0.29535381929129 | | 2004 | 3.2211807849702 | | 2003 | 0.23913445705037 | | 2002 | 0.32757192863083 | | 2001 | 1.438927459752 | | 2000 | 1.4154820273693 | | 1999 | 1.8309495267628 | | 1998 | 2.1438888435923 | | 1997 | 1.0438755037447 | | 1996 | 0.71494261562543 | | 1995 | 1.7019702098207 | | 1994 | 2.4262281116496 | | 1993 | -1.3716993254559 | | 1992 | 2.4177731791505 | | 1991 | 3.7936077151927 | | 1990 | 5.5578302948267 | | 1989 | 3.3600238545016 | | 1988 | 4.4130884314086 | | 1987 | 2.1076882766834 | | 1986 | 5.5112878469558 | | 1985 | 2.5363975932631 | | 1984 | 2.7743334963116 | | 1983 | 2.2991553883137 | | 1982 | 0.46953648643324 | | 1981 | -1.8291758507527 | | 1980 | 0.86662409634697 | | 1979 | 2.6162510438118 | | 1978 | 4.1524379063128 | | 1977 | 3.2400540604863 | | 1976 | 4.7939184626744 | | 1975 | 0.85184135784444 | | 1974 | 0.85873946626542 | | 1973 | 4.505610580439 | | 1972 | 4.2781084795353 | | 1971 | 3.1602587494527 |
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