| Year | Value | | 2021 | 1.7538599034911 | | 2020 | 5.9254314328809 | | 2019 | 5.2696692030071 | | 2018 | 3.5285249824525 | | 2017 | -5.6317457479432 | | 2016 | 4.7953900724676 | | 2015 | 8.8265361149112 | | 2014 | 3.3210487107352 | | 2013 | 3.1238743279688 | | 2012 | 5.1659995335234 | | 2011 | 2.4725720607545 | | 2010 | 3.7154530395761 | | 2009 | 6.3485589233662 | | 2008 | 3.7773674705227 | | 2007 | 7.3760068699789 | | 2006 | 8.5900773642141 | | 2005 | 1.8581009563268 | | 2004 | 1.453262527065 | | 2003 | 0.92151209425579 | | 2002 | 1.2519775851093 | | 2001 | 8.1480082341923 | | 2000 | 6.7623345466621 | | 1999 | 3.9942609473262 | | 1998 | 0.84171204173906 | | 1997 | 9.2315872005722 | | 1996 | 6.1643232950406 | | 1995 | 5.2104721228049 | | 1994 | 6.1250262735448 | | 1993 | 0.36921183457498 | | 1992 | 8.8817054833721 | | 1991 | 17.53170221158 | | 1990 | 0.18286838886034 | | 1989 | 1.2229763470914 | | 1988 | -1.7973840071223 | | 1987 | 8.1440783419543 | | 1986 | 16.953752437795 | | 1985 | 4.957834474744 | | 1984 | 5.7892581078514 | | 1983 | 8.8943622697056 | | 1982 | 16.475505662693 | | 1981 | 7.6117950019148 | | 1980 | 6.4949685607113 | | 1979 | -20.009283796914 | | 1978 | -6.3370311136431 | | 1977 | 0.80993945444912 | | 1976 | 13.480942410436 | | 1975 | -3.4110652418926 | | 1974 | -8.1494927829328 | | 1973 | 2.1889332336257 | | 1972 | 3.1198603605386 | | 1971 | 1.896173964111 |
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