| Year | Value | | 2021 | 4.8430998989107 | | 2020 | -5.0687710518739 | | 2019 | 1.6452385618424 | | 2018 | 1.9905608586109 | | 2017 | 2.6217223355959 | | 2016 | 1.7055608692738 | | 2015 | 3.1888652524306 | | 2014 | 2.6532770458489 | | 2013 | 1.4325034717762 | | 2012 | 1.7734102029508 | | 2011 | 1.4641454254048 | | 2010 | 3.9355820676013 | | 2009 | -2.6096107255443 | | 2008 | -2.0727239252173 | | 2007 | 1.6536600001421 | | 2006 | 3.1777222199923 | | 2005 | 2.3233026877301 | | 2004 | 3.3270343367395 | | 2003 | 1.7258426278888 | | 2002 | 1.3114208257871 | | 2001 | 1.649790949276 | | 2000 | 3.5187222722611 | | 1999 | 3.1822136176346 | | 1998 | 3.6303439427877 | | 1997 | 4.032460816421 | | 1996 | 3.2846210537976 | | 1995 | 2.8664991217174 | | 1994 | 3.9177689295579 | | 1993 | 0.95901545733604 | | 1992 | 2.2138393931893 | | 1991 | 1.5326393847381 | | 1990 | 2.6468733996448 | | 1989 | 3.1522411897576 | | 1988 | 5.3286897986554 | | 1987 | 3.7023734913168 | | 1986 | 4.0630341468144 | | 1985 | 3.8679882975008 | | 1984 | 5.1181088468001 | | 1983 | 2.2011217610815 | | 1982 | 0.97205460302202 | | 1981 | 1.9909179610891 | | 1980 | 0.46197609165576 | | 1979 | 1.6445847478219 | | 1978 | 4.8004614867201 | | 1977 | 3.3266566776353 | | 1976 | 4.7392974255882 | | 1975 | 0.41623070892447 | | 1974 | -2.3006834892665 | | 1973 | 5.707291678795 | | 1972 | 5.5587878518732 | | 1971 | 3.2447321495647 |
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