| Year | Value | | 2021 | 10.470134459928 | | 2020 | -6.8623120688998 | | 2019 | 2.7807680025878 | | 2018 | 5.9134198761034 | | 2017 | 8.756344359408 | | 2016 | 7.4943818364664 | | 2015 | 9.0774568238173 | | 2014 | 6.4735019130139 | | 2013 | 6.2117490857675 | | 2012 | 6.0851930901907 | | 2011 | 4.7446901798184 | | 2010 | 9.7996781676192 | | 2009 | 9.8622059459306 | | 2008 | 2.7555737911416 | | 2007 | 8.2116405739635 | | 2006 | 8.3156482150583 | | 2005 | 8.5132797498025 | | 2004 | 8.9862942378965 | | 2003 | 9.6197123894364 | | 2002 | 4.9748536484913 | | 2001 | 1.07676726307 | | 2000 | 5.5074933869846 | | 1999 | 2.6689469005742 | | 1998 | 6.9717007011521 | | 1997 | 3.3355667726019 | | 1996 | 12.525124674832 | | 1995 | 4.7992606036186 | | 1994 | 5.6165142098879 | | 1993 | 9.9841935480936 | | 1992 | 4.150056185727 | | 1991 | 0.75520581333181 | | 1990 | 7.7580947027977 | | 1989 | 6.1983156482218 | | 1988 | 8.4764246030626 | | 1987 | 6.7740839562993 | | 1986 | 4.1517819206495 | | 1985 | 2.7876098958256 | | 1984 | 1.713174651738 | | 1983 | 11.574525217347 | | 1982 | 1.9460842436063 | | 1981 | -2.6216365612823 | | 1980 | 11.712665443013 | | 1979 | -4.1794604836894 | | 1978 | 6.83191407313 | | 1977 | 6.0311102690322 | | 1976 | 8.0491085332513 | | 1975 | 7.2602831769687 | | 1974 | -7.424974839181 |
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