| Year | Value | | 2021 | 2.5640400434104 | | 2020 | -11.431865426109 | | 2019 | 1.2344121642197 | | 2018 | 1.2135495120252 | | 2017 | 2.4822049533553 | | 2016 | 1.3618278055511 | | 2015 | 4.7492122815809 | | 2014 | 4.5645187399516 | | 2013 | 0.9490458203439 | | 2012 | 2.1448139878584 | | 2011 | 2.8909489134086 | | 2010 | 4.7756155355435 | | 2009 | -6.3027271088702 | | 2008 | -1.1771113847606 | | 2007 | 1.9592963343186 | | 2006 | 6.7674696174434 | | 2005 | 0.72177093324434 | | 2004 | 3.0573765904864 | | 2003 | -2.3029247264119 | | 2002 | 0.10903860442153 | | 2001 | 1.2738321351828 | | 2000 | 4.6276593299101 | | 1999 | 5.7098871303219 | | 1998 | 4.7466050691056 | | 1997 | 10.933014870334 | | 1996 | 6.0766227736234 | | 1995 | -11.33736270327 | | 1994 | 7.7136295614572 | | 1993 | -1.0213822642764 | | 1992 | 4.6770372985287 | | 1991 | 8.1035085436737 | | 1990 | 7.3599125284993 | | 1989 | 6.2979052906121 | | 1988 | -2.3155863932247 | | 1987 | 4.4666612559992 | | 1986 | -10.992327848152 | | 1985 | 5.2103421151589 | | 1984 | 2.9911622896505 | | 1983 | -12.424764502059 | | 1982 | -6.8007293143526 | | 1981 | 10.359121067789 | | 1980 | 14.484085170286 | | 1979 | 7.4863367112515 | | 1978 | 7.7261765732846 | | 1977 | 0.26384466285549 | | 1976 | 3.6501936077559 | | 1975 | 3.2130716310101 | | 1974 | 5.8097366717282 | | 1973 | 9.2338420629841 | | 1972 | 8.7113829480483 | | 1971 | 4.0708108738317 |
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