| Year | Value | | 2014 | -54.601627539432 | | 2013 | -53.478924050031 | | 2012 | -50.850349820232 | | 2011 | -24.981523840833 | | 2010 | -22.551643790175 | | 2009 | -22.174784423635 | | 2008 | -23.28186217973 | | 2007 | -21.289739037659 | | 2006 | -22.654326784658 | | 2005 | -18.700681077496 | | 2004 | -8.1607942994803 | | 2003 | 4.1118151367525 | | 2002 | -1.542664671344 | | 2001 | 0.02465991250965 | | 2000 | -1.1908524529963 | | 1999 | -2.5480420378326 | | 1998 | -1.728287542826 | | 1997 | 6.5845680264333 | | 1996 | 6.1662996203734 | | 1995 | 5.9935700262145 | | 1994 | 5.6306328277527 | | 1993 | 6.3484336220287 | | 1992 | 5.6675891274704 | | 1991 | 4.9397708300569 | | 1990 | 5.299956264997 | | 1989 | 7.1411842119938 | | 1988 | 7.3314995577842 | | 1987 | 7.3457141088827 | | 1986 | 7.5673559101115 | | 1985 | 6.9518160548649 | | 1984 | 6.9946177686968 | | 1983 | 7.8864701699616 | | 1982 | 7.5292473621335 | | 1981 | 6.5598900138932 | | 1980 | 9.4281138221811 | | 1979 | 7.3386150750497 | | 1978 | 7.2606720035769 | | 1977 | 8.6509119582265 | | 1976 | 5.1053165204237 | | 1975 | 6.0269787188177 | | 1974 | 8.2911311298008 | | 1973 | 9.8278342899893 | | 1972 | 9.4677662421308 | | 1971 | 10.596851693524 |
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