| Year | Value | | 2014 | 7.0775386886229 | | 2013 | 4.5973747490517 | | 2012 | 1.1348920611306 | | 2011 | -5.4519749960176 | | 2010 | -9.8641855482072 | | 2009 | -15.416667111021 | | 2008 | -11.559949653602 | | 2007 | -12.965546533559 | | 2006 | -26.256389057314 | | 2005 | -10.499895565066 | | 2004 | -2.6618192720606 | | 2003 | -2.7701706755885 | | 2002 | 6.4657417823775 | | 2001 | 8.5270461920081 | | 2000 | 11.450978543977 | | 1999 | 14.239382050318 | | 1998 | 8.1262230338537 | | 1997 | 7.8929103114463 | | 1996 | 10.894245382 | | 1995 | 17.585944360604 | | 1994 | 21.709743464448 | | 1993 | 22.175132290643 | | 1992 | 22.3336296007 | | 1991 | 22.661068430075 | | 1990 | 22.15424299179 | | 1989 | 25.192831149219 | | 1988 | 15.892092746939 | | 1987 | 10.618560879714 | | 1986 | 6.9355335223588 | | 1985 | -2.8092827910366 | | 1984 | -2.7886198538962 | | 1983 | -4.1614840684664 | | 1982 | 6.8262618596683 | | 1981 | 20.007844538774 | | 1980 | 32.318210816135 | | 1979 | 37.127873902085 | | 1978 | 39.937900910503 | | 1977 | 37.840491204861 | | 1976 | 38.476590901114 | | 1975 | 35.83681301604 | | 1974 | 34.923758483393 | | 1973 | 34.667791370008 | | 1972 | 34.600117079163 | | 1971 | 33.228577713327 |
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