| Year | Value | | 2021 | 10.359453849784 | | 2020 | -6.9101744103015 | | 2019 | 2.7807679929434 | | 2018 | 5.9134229728959 | | 2017 | 8.756342380384 | | 2016 | 7.4943806629154 | | 2015 | 9.0774568046451 | | 2014 | 6.4735062971181 | | 2013 | 6.2117447298493 | | 2012 | 6.0851926796738 | | 2011 | 4.1690436238527 | | 2010 | 9.3744339229473 | | 2009 | 11.111833020064 | | 2008 | 1.7552307071815 | | 2007 | 8.4884954372492 | | 2006 | 7.6884001981492 | | 2005 | 8.5116423288203 | | 2004 | 10.20600231901 | | 2003 | 9.6197116190052 | | 2002 | 4.9752858241323 | | 2001 | 1.0764588948258 | | 2000 | 5.507478940136 | | 1999 | 2.6690890549313 | | 1998 | 6.9717007011521 | | 1997 | 3.3355667726019 | | 1996 | 12.525124674832 | | 1995 | 4.7994975874583 | | 1994 | 5.6162753785228 | | 1993 | 9.9841935480936 | | 1992 | 4.150056185727 | | 1991 | 0.75520581333181 | | 1990 | 7.7580947027977 | | 1989 | 6.1983156482218 | | 1988 | 8.4764246030626 | | 1987 | 6.7740839562993 | | 1986 | 4.1517819206495 | | 1985 | 2.7876098958256 | | 1984 | 1.713174651738 | | 1983 | 11.574525217347 | | 1982 | 1.9460842436063 | | 1981 | -2.6233268151581 | | 1980 | 11.71183809395 | | 1979 | -4.1785004761347 | | 1978 | 6.8334893274753 | | 1977 | 6.0318457476844 | | 1976 | 8.0472228149675 | | 1975 | 7.2606580215347 | | 1974 | -7.4269267885368 | | 1973 | 7.5698890719317 | | 1972 | 0.25683644470797 | | 1971 | 1.4064474757503 |
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