| Year | Value | | 2021 | 1.088 | | 2020 | 1.072 | | 2019 | 1.077 | | 2018 | 1.104 | | 2017 | 1.123 | | 2016 | 1.175 | | 2015 | 1.196 | | 2014 | 1.224 | | 2013 | 1.199 | | 2012 | 1.184 | | 2011 | 1.115 | | 2010 | 1.042 | | 2009 | 0.986 | | 2008 | 0.947 | | 2007 | 0.918 | | 2006 | 0.874 | | 2005 | 0.834 | | 2004 | 0.8 | | 2003 | 0.792 | | 2002 | 0.8 | | 2001 | 0.84 | | 2000 | 0.912 | | 1999 | 0.991 | | 1998 | 1.073 | | 1997 | 1.163 | | 1996 | 1.254 | | 1995 | 1.341 | | 1994 | 1.42 | | 1993 | 1.48 | | 1992 | 1.567 | | 1991 | 1.638 | | 1990 | 1.74 | | 1989 | 1.814 | | 1988 | 1.838 | | 1987 | 1.943 | | 1986 | 2.041 | | 1985 | 2.101 | | 1984 | 2.074 | | 1983 | 2.036 | | 1982 | 1.964 | | 1981 | 1.874 | | 1980 | 1.782 | | 1979 | 1.664 | | 1978 | 1.561 | | 1977 | 1.536 | | 1976 | 1.542 | | 1975 | 1.597 | | 1974 | 1.685 | | 1973 | 1.772 | | 1972 | 1.866 | | 1971 | 1.961 | | 1970 | 2.095 | | 1969 | 2.349 | | 1968 | 2.677 | | 1967 | 3.086 | | 1966 | 3.473 | | 1965 | 3.838 | | 1964 | 4.16 | | 1963 | 4.393 | | 1962 | 4.533 | | 1961 | 4.731 | | 1960 | 4.933 |
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