| Year | Value | | 2021 | 5.0630966839346 | | 2020 | -9.0300818174776 | | 2019 | 3.6662529965818 | | 2018 | 4.9089781995649 | | 2017 | 7.389087516924 | | 2016 | 4.7995317206829 | | 2015 | 7.6299033471291 | | 2014 | -3.7106678287406 | | 2013 | -8.2663220808744 | | 2012 | -7.2907605848277 | | 2011 | 4.4992781688984 | | 2010 | 0.38319342380062 | | 2009 | 0.62527654001111 | | 2008 | 8.7039326945785 | | 2007 | 4.8001203316098 | | 2006 | 3.9296752063738 | | 2005 | 3.9775665069968 | | 2004 | 3.8175178255544 | | 2003 | 6.184046186762 | | 2002 | 4.5907689404126 | | 2001 | 7.8227082162019 | | 2000 | 2.8130816112209 | | 1999 | -3.9397104861129 | | 1998 | 18.382058567927 | | 1997 | 1.5150309956508 | | 1996 | 0.93507972683575 | | 1995 | 4.8031381337699 | | 1994 | 6.6732391611496 | | 1993 | -6.7999560455314 | | 1992 | 13.796296750363 | | 1991 | -3.0013776766279 | | 1990 | 3.9984080193752 | | 1989 | 10.982702120775 | | 1988 | 9.9051421554132 | | 1987 | 9.4207569769556 | | 1986 | 0.37442174252553 | | 1985 | 4.949699321847 | | 1984 | 13.092107426069 | | 1983 | 3.913165886291 | | 1982 | 7.5785674372767 | | 1981 | -1.8432234447344 | | 1980 | 5.6117273296343 | | 1979 | 14.708587949771 | | 1978 | 6.3695242684524 | | 1977 | 21.72447364503 |
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