| Year | Value | | 2014 | 13.0293607429 | | 2013 | 12.688577630342 | | 2012 | 6.1414479605977 | | 2011 | 3.217909197688 | | 2010 | -1.072041291755 | | 2009 | -7.3545132056414 | | 2008 | -6.2315927509542 | | 2007 | -12.669946576214 | | 2006 | -18.158819009166 | | 2005 | -26.542802547991 | | 2004 | -29.824428220494 | | 2003 | -41.417182524821 | | 2002 | -45.622126018228 | | 2001 | -45.535109372505 | | 2000 | -34.652563369761 | | 1999 | -32.320275667854 | | 1998 | -32.971480652557 | | 1997 | -32.776033900158 | | 1996 | -29.506467943515 | | 1995 | -24.20044554812 | | 1994 | -17.169829601933 | | 1993 | -14.066630290583 | | 1992 | -8.7813679609281 | | 1991 | -5.7546208283955 | | 1990 | -5.1097117210256 | | 1989 | -1.5773549433078 | | 1988 | 3.3195823452168 | | 1987 | 6.3814938401114 | | 1986 | 2.2690060431293 | | 1985 | -2.9173039054955 | | 1984 | 0.89450900804011 | | 1983 | 0.40850072677742 | | 1982 | 2.6515429580326 | | 1981 | 3.3733931866834 | | 1980 | 7.1687149532828 | | 1979 | 11.555825491168 | | 1978 | 12.84370112643 | | 1977 | 14.363199389422 | | 1976 | 16.545056720852 | | 1975 | 14.743830102228 | | 1974 | 14.955340234775 | | 1973 | 14.226956732456 | | 1972 | 9.4541984493968 | | 1971 | 9.1835782765625 |
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