| Year | Value | | 2021 | 6.3937397720375 | | 2020 | 0.53796658072176 | | 2019 | 1.1890679238703 | | 2018 | 2.0629610652951 | | 2017 | 2.7006775572239 | | 2016 | 2.362527511845 | | 2015 | 2.628831575376 | | 2014 | 3.5773753515518 | | 2013 | 3.2246326702198 | | 2012 | 0.84202552742978 | | 2011 | 0.75838154314836 | | 2010 | 4.7972971305018 | | 2009 | -4.1285368393115 | | 2008 | 0.62090501236035 | | 2007 | 0.65287094630718 | | 2006 | 4.3075509288167 | | 2005 | 4.1729923557769 | | 2004 | 4.2174393736574 | | 2003 | 0.56562288041677 | | 2002 | 0.61419425719306 | | 2001 | 1.5140532872605 | | 2000 | 2.1360070489151 | | 1999 | 2.7489932032049 | | 1998 | 2.7217818916663 | | 1997 | 3.0706748299133 | | 1996 | 3.2636912106972 | | 1995 | 3.4644344567918 | | 1994 | 5.5512227581018 | | 1993 | 0.021418157078983 | | 1992 | 3.3517677137879 | | 1991 | 0.75513688272437 | | 1990 | 1.29519053262 | | 1989 | 0.27073334346414 | | 1988 | -1.2651373443068 | | 1987 | 0.59026476688678 | | 1986 | 7.3261915856365 | | 1985 | 4.0087834868675 | | 1984 | 3.5077117502098 | | 1983 | 3.1228368113337 | | 1982 | 2.2990656367608 | | 1981 | -2.8993412950727 | | 1980 | -3.6007334896931 | | 1979 | 1.4467490984327 | | 1978 | 4.0926609592737 | | 1977 | 2.5897490883073 | | 1976 | 6.4593037608316 | | 1975 | 0.91780566747219 | | 1974 | -5.4541333994591 | | 1973 | 7.0436936046248 | | 1972 | 4.2927321583443 | | 1971 | 2.2297113796897 |
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