| Year | Value | | 2022 | 17.689209558815 | | 2021 | 0.39134674830079 | | 2020 | 9.8503990227421 | | 2019 | 3.3478765503765 | | 2018 | 0.3112101603907 | | 2017 | 8.2795367226083 | | 2016 | 7.1743430198201 | | 2015 | 2.5285028419242 | | 2014 | 2.3544905282036 | | 2013 | 5.9242686798485 | | 2012 | 10.271018231888 | | 2011 | 3.0801706924026 | | 2010 | 0.24612869343693 | | 2009 | 12.944397840171 | | 2008 | 15.438213870925 | | 2007 | 9.0807220587316 | | 2006 | 8.8828265477792 | | 2005 | 9.0140891809234 | | 2004 | 12.250710289439 | | 2003 | 7.4497001400737 | | 2002 | 1.9925854245399 | | 2001 | 3.3428550674941 | | 2000 | 3.8995298028471 | | 1999 | -2.4059320974226 | | 1998 | 6.2100670945581 | | 1997 | 12.015422519569 | | 1996 | 7.4113717352664 | | 1993 | 12.354388763045 | | 1992 | 9.5604118760082 | | 1991 | 19.637165814837 | | 1990 | 4.1857637264995 | | 1989 | 1.0102782483111 | | 1988 | 2.9786435565803 | | 1987 | 4.1330149080913 | | 1986 | -1.1170665728068 | | 1985 | 1.7593300565169 | | 1984 | 5.3695703882738 | | 1983 | 6.5930021430708 | | 1982 | 12.565136533413 | | 1981 | 6.4506644718119 | | 1980 | 7.2493929932527 | | 1979 | 15.673329442373 | | 1978 | 13.270533797388 | | 1977 | 13.655146506643 | | 1976 | 7.1658615138318 | | 1975 | 30.226046574907 | | 1974 | 31.088299365448 | | 1973 | 9.3736740756774 | | 1972 | 3.092193808935 | | 1971 | 0.48858007422289 | | 1970 | 0.51488580802246 | | 1969 | 0.48493955331757 | | 1968 | 3.1619369726993 | | 1967 | 1.4529273002285 |
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