| Year | Value | | 2020 | 18.6340384479 | | 2019 | 13.11521306831 | | 2018 | 15.087718262424 | | 2017 | 15.119569750825 | | 2016 | 9.7110562324554 | | 2015 | 11.436781925775 | | 2014 | 10.494488279973 | | 2013 | 15.428562935078 | | 2012 | 15.516326269459 | | 2011 | 18.51227022775 | | 2010 | 13.788966924967 | | 2009 | 12.986096403398 | | 2008 | 11.77699392823 | | 2007 | 15.364817793194 | | 2006 | 12.729266714099 | | 2005 | 2.7018152744195 | | 2004 | 16.883420119808 | | 2003 | 22.182337126271 | | 2002 | -4.5029064959751 | | 2001 | -19.643625370567 | | 2000 | -6.7889621931232 | | 1999 | 6.1890614845613 | | 1998 | 7.7168371553924 | | 1997 | -7.4816820102242 | | 1996 | -10.536681413917 | | 1995 | -7.5692770786689 | | 1994 | -13.569788363564 | | 1993 | -27.526980478667 | | 1992 | -17.941982852142 | | 1991 | -44.937272903141 | | 1990 | -34.896642184123 | | 1989 | -59.788644465356 | | 1988 | -77.55282571872 | | 1987 | -18.866892141477 | | 1986 | -55.204416742033 | | 1985 | -124.76184751842 | | 1984 | -126.01382790486 | | 1983 | -125.99940899736 | | 1982 | -128.95679323671 | | 1981 | -124.9175268379 | | 1980 | -125.98518145805 |
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