| Year | Value | | 2015 | 20.969042498326 | | 2014 | -2.4598593943822 | | 2013 | -3.0671847766684 | | 2012 | -2.7334129538837 | | 2011 | -3.1297424665366 | | 2010 | -2.0950109169655 | | 2009 | -2.8918876494154 | | 2008 | -2.9570103303466 | | 2007 | -2.2022056284063 | | 2006 | -3.1630154941738 | | 2005 | -3.19811273266 | | 2004 | -2.7325007780543 | | 2003 | -2.4335994367622 | | 2002 | -1.9438499552447 | | 2001 | -3.2675664582432 | | 2000 | -2.8029489530746 | | 1999 | -2.1147668397592 | | 1998 | -4.0617105657266 | | 1997 | -3.3376896508886 | | 1996 | -2.9528602977821 | | 1995 | -3.0464017811342 | | 1994 | -3.1343766331802 | | 1993 | -2.3372147601187 | | 1992 | -3.0501049038558 | | 1991 | -2.4003612752008 | | 1990 | -2.8905382749209 | | 1989 | 1.0028918484662 | | 1988 | 1.4032116360944 | | 1987 | 1.7096100724086 | | 1986 | 0.7004224589828 | | 1985 | 1.6780896225293 | | 1984 | 0.67986312531996 | | 1983 | 2.0077848235185 | | 1982 | 1.038766336391 | | 1981 | 0.2253332051697 | | 1980 | 0.86184989126462 | | 1979 | -1.4731767948732 | | 1978 | 0.44999708349033 | | 1977 | -1.6803498678448 | | 1976 | -1.5475857056623 | | 1975 | -2.141647041835 | | 1974 | -3.5666249254756 | | 1973 | -3.4145486871004 | | 1972 | -3.230226003395 | | 1971 | -3.6765976763699 | | 1970 | 29.500019091911 | | 1969 | 29.326784816325 | | 1968 | 26.67112704951 | | 1967 | 24.685404332634 | | 1966 | 24.519813302689 | | 1965 | 23.691339857821 | | 1964 | 21.961508102703 | | 1963 | 21.140441622018 | | 1962 | 19.022630300248 | | 1961 | 17.635803486572 | | 1960 | 16.716146904006 |
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