| Year | Value | | 2014 | -10.992737132779 | | 2013 | -15.379065419401 | | 2012 | -12.885422777874 | | 2011 | -27.405909994091 | | 2010 | -24.1934568445 | | 2009 | -19.107389735186 | | 2008 | -18.366745012253 | | 2007 | -22.249683095518 | | 2006 | -20.354217595489 | | 2005 | -23.123196466483 | | 2004 | -27.612904441786 | | 2003 | -34.605775403616 | | 2002 | -36.20910004179 | | 2001 | -34.190887598287 | | 2000 | -33.745153153629 | | 1999 | -29.097803403378 | | 1998 | -27.23598194321 | | 1997 | -27.742168518999 | | 1996 | -27.678850157122 | | 1995 | -28.653826364569 | | 1994 | -27.872087379847 | | 1993 | -19.99518676589 | | 1992 | -15.684721116589 | | 1991 | -14.93116084717 | | 1990 | -10.493237724706 | | 1989 | -8.8063877782509 | | 1988 | -4.2455964053828 | | 1987 | 2.7893833706016 | | 1986 | 5.8533189669685 | | 1985 | 6.3984921705204 | | 1984 | 7.0591974076306 | | 1983 | 6.5020944466202 | | 1982 | 4.5849081012305 | | 1981 | 2.9329092788732 | | 1980 | 2.838054820496 | | 1979 | 3.7344830724461 | | 1978 | 0.32786184058958 | | 1977 | 0.27201897255831 | | 1976 | -2.4099441749227 | | 1975 | 0.89574206396363 | | 1974 | 4.4772769116018 | | 1973 | 5.266418945829 | | 1972 | 3.5759007409807 | | 1971 | 5.4293320026437 |
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