| Year | Value | | 2021 | 3.6322760068821 | | 2020 | -6.5959246217801 | | 2019 | 1.5051168361382 | | 2018 | 2.0937273840209 | | 2017 | 0.35264930518646 | | 2016 | 3.762289765364 | | 2015 | 0.53542901814984 | | 2014 | 0.87709198339594 | | 2013 | 0.23920548650678 | | 2012 | 0.40137443875075 | | 2011 | 1.5346834172237 | | 2010 | 1.9125010751141 | | 2009 | -5.0579959805433 | | 2008 | 1.5550605120108 | | 2007 | 3.4004017590718 | | 2006 | 4.1302946553504 | | 2005 | 1.8372248775446 | | 2004 | 3.0023880793511 | | 2003 | 0.91698222981789 | | 2002 | 2.6265794493337 | | 2001 | 0.23305730990157 | | 2000 | 3.6917883936221 | | 1999 | 1.916619048688 | | 1998 | 3.3614146280341 | | 1997 | 1.4211196756835 | | 1996 | 2.1946805029232 | | 1995 | 2.1523071297653 | | 1994 | 2.414466554205 | | 1993 | 0.068890122347568 | | 1992 | 2.0048996009434 | | 1991 | 2.9393006224082 | | 1990 | 4.481452876591 | | 1989 | 3.8300698185333 | | 1988 | 3.9097740870274 | | 1987 | 1.8884107752613 | | 1986 | 2.7385127699498 | | 1985 | 2.1832536409847 | | 1984 | 0.16175283747404 | | 1983 | 3.6276542615204 | | 1982 | 1.9330095680256 | | 1981 | 0.80312201525469 | | 1980 | 0.79378744115901 | | 1979 | 5.0193430965964 | | 1978 | 0.39703145325399 | | 1977 | 4.6526295779134 | | 1976 | 4.4736157113124 | | 1975 | 0.029544732899069 | | 1974 | 2.0440199051541 | | 1973 | 5.9850223968884 | | 1972 | 6.4095759264857 | | 1971 | 4.5744753214766 |
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