| Year | Value | | 2015 | 6.6118159324936 | | 2014 | -9.2362586619434 | | 2013 | -23.200136741845 | | 2012 | -25.569707147505 | | 2011 | -29.829706305468 | | 2010 | -29.367732560307 | | 2009 | -33.873091110527 | | 2008 | -32.272607903831 | | 2007 | -36.535262519701 | | 2006 | -42.905321378295 | | 2005 | -44.938423412643 | | 2004 | -45.712289277514 | | 2003 | -42.575246772566 | | 2002 | -42.92727186923 | | 2001 | -44.158308179242 | | 2000 | -44.243159147439 | | 1999 | -41.555545313755 | | 1998 | -44.996606951778 | | 1997 | -47.342731897228 | | 1996 | -45.871833669313 | | 1995 | -41.697509812659 | | 1994 | -37.092454063543 | | 1993 | -39.800473939168 | | 1992 | -37.430990427485 | | 1991 | -40.151988851667 | | 1990 | -38.79232608377 | | 1989 | -34.859143431048 | | 1988 | -35.753697883559 | | 1987 | -34.769652183452 | | 1986 | -36.373464310041 | | 1985 | -38.434656732142 | | 1984 | -41.438109929 | | 1983 | -40.476981703464 | | 1982 | -39.094336027835 | | 1981 | -36.144041577974 | | 1980 | -30.811671227574 | | 1979 | -29.513386257959 | | 1978 | -24.858272559204 | | 1977 | -26.130219085083 | | 1976 | -27.288128943972 | | 1975 | -31.41175039423 | | 1974 | -46.009904299976 | | 1973 | -59.400925506296 | | 1972 | -61.669031290892 | | 1971 | -74.31734838055 |
|