| Year | Value | | 2021 | 0.67331898019818 | | 2020 | -3.7170135956577 | | 2019 | 6.9986026565929 | | 2018 | 2.3741650753924 | | 2017 | 5.0239860277294 | | 2016 | 4.2741537896768 | | 2015 | 8.1538471408161 | | 2014 | 2.4609308699253 | | 2013 | 1.6486955096774 | | 2012 | 2.911542905085 | | 2011 | 7.7788607984319 | | 2010 | 11.892979786833 | | 2009 | -6.622003937771 | | 2008 | 7.4704632272336 | | 2007 | 10.21368853179 | | 2006 | 10.573549876473 | | 2005 | 1.1861020706731 | | 2004 | 15.133740635434 | | 2003 | 3.5128698855066 | | 2002 | 16.262948998969 | | 2001 | -5.697037711838 | | 2000 | 11.092502618126 | | 1999 | 8.3423149456026 | | 1998 | -10.629714572947 | | 1997 | 9.5783859806594 | | 1996 | 8.941810694439 | | 1995 | 18.72471419109 | | 1994 | 7.631824331612 | | 1993 | 20.246260987942 | | 1992 | 2.7251076440754 | | 1991 | 24.222989196069 | | 1990 | 11.924835983401 | | 1989 | 2.3531899529853 | | 1988 | 22.387143580691 | | 1987 | 4.0336925942399 | | 1986 | -10.569956080743 | | 1985 | -15.602994323078 | | 1984 | 29.504734551937 | | 1983 | 8.1074785092594 | | 1982 | -3.3276348501591 | | 1981 | 18.146696523126 | | 1980 | 8.0243515089262 | | 1979 | -7.2330985672578 | | 1978 | 13.711222010519 | | 1977 | 12.835854528891 | | 1976 | 23.915095493373 | | 1975 | -21.583647542158 | | 1974 | 35.429303269966 | | 1973 | 14.772437684957 | | 1972 | -9.4457765155144 | | 1971 | -8.1548893806212 |
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