| Year | Value | | 2021 | 1.2272314415924 | | 2020 | -3.2163247778803 | | 2019 | 0.74604751009465 | | 2018 | 1.8467597543078 | | 2017 | 6.0538930380489 | | 2016 | 5.8113918553212 | | 2009 | 11.408415849379 | | 2008 | 1.8077480081952 | | 2007 | 5.9023002412907 | | 2006 | 6.1049016734166 | | 2005 | 3.5761628183224 | | 2004 | 1.6381354926848 | | 2003 | 10.942555741874 | | 2002 | 4.3765561165694 | | 2001 | 2.648545849113 | | 2000 | 3.9359073893265 | | 1999 | 4.1558250259748 | | 1998 | 6.9752341159064 | | 1997 | 6.536317492335 | | 1996 | 5.2688272723658 | | 1995 | 0.88295498481852 | | 1994 | 4.9483831757363 | | 1993 | 7.3695532024117 | | 1992 | 3.8899610328544 | | 1991 | 5.838338923716 | | 1990 | -4.6822103769814 | | 1989 | 3.0697120820018 | | 1988 | 0.38188789967822 | | 1987 | 2.8632485854789 | | 1986 | 1.9379855031514 | | 1985 | 5.6348769448106 | | 1984 | 8.513772394639 | | 1983 | 9.0095315619508 | | 1982 | 1.615415532737 | | 1981 | 21.910080274917 | | 1980 | 6.9028876845726 | | 1979 | 20.080363444639 | | 1978 | 10.981305981423 | | 1977 | 9.8762597670815 | | 1976 | 1.2530810696247 | | 1975 | -2.4985167187992 | | 1974 | 10.698450401596 | | 1973 | 5.0959546494483 | | 1972 | 0.62529481701168 |
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