| Year | Value | | 2015 | 42.152562658039 | | 2014 | -13.745040775635 | | 2013 | -14.636310244531 | | 2012 | -14.782849522005 | | 2011 | -16.687857748317 | | 2010 | -17.784017771146 | | 2009 | -18.812719483397 | | 2008 | -21.037425505501 | | 2007 | -21.0812000058 | | 2006 | -22.809243363356 | | 2005 | -24.892600150103 | | 2004 | -25.363801400739 | | 2003 | -26.32099752834 | | 2002 | -25.859262926285 | | 2001 | -26.692106025626 | | 2000 | -26.237634944662 | | 1999 | -23.926491463791 | | 1998 | -24.973530369049 | | 1997 | -23.540586017081 | | 1996 | -22.897439797272 | | 1995 | -23.190879365975 | | 1994 | -23.561950424579 | | 1993 | -20.867383569532 | | 1992 | -21.721326384913 | | 1991 | -19.23691957389 | | 1990 | -21.025363045019 | | 1989 | -14.548186647311 | | 1988 | -10.850937841954 | | 1987 | -11.043155515458 | | 1986 | -12.385561603802 | | 1985 | -12.235016917351 | | 1984 | -13.058400493152 | | 1983 | -10.655093765362 | | 1982 | -8.2504481500374 | | 1981 | -9.2725146081416 | | 1980 | -12.968427916272 | | 1979 | -19.194013460397 | | 1978 | -17.903679041856 | | 1977 | -19.913086613381 | | 1976 | -23.094588920403 | | 1975 | -22.748221919004 | | 1974 | -27.080890488357 | | 1973 | -30.342636561898 | | 1972 | -31.750902259587 | | 1971 | -30.64660201684 | | 1970 | -8.243641009634 | | 1969 | -8.9050634094995 | | 1968 | -9.4657618361437 | | 1967 | -9.0782321790452 | | 1966 | -11.071026511622 | | 1965 | -11.229933440723 | | 1964 | -13.270191288366 | | 1963 | -10.931869236296 | | 1962 | -8.9512536440363 | | 1961 | -11.579360701573 | | 1960 | -13.507026696638 |
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