| Year | Value | | 2021 | 1.48 | | 2020 | 1.48 | | 2019 | 1.52 | | 2018 | 1.49 | | 2017 | 1.49 | | 2016 | 1.46 | | 2015 | 1.46 | | 2014 | 1.46 | | 2013 | 1.43 | | 2012 | 1.45 | | 2011 | 1.4 | | 2010 | 1.4 | | 2009 | 1.44 | | 2008 | 1.4 | | 2007 | 1.38 | | 2006 | 1.43 | | 2005 | 1.45 | | 2004 | 1.57 | | 2003 | 1.59 | | 2002 | 1.57 | | 2001 | 1.58 | | 2000 | 1.48 | | 1999 | 1.257 | | 1998 | 1.195 | | 1997 | 1.559 | | 1996 | 1.644 | | 1995 | 1.686 | | 1994 | 1.66 | | 1993 | 1.702 | | 1992 | 1.678 | | 1991 | 1.73 | | 1990 | 1.743 | | 1989 | 1.733 | | 1988 | 1.832 | | 1987 | 1.834 | | 1986 | 1.82 | | 1985 | 1.839 | | 1984 | 1.898 | | 1983 | 1.829 | | 1982 | 1.837 | | 1981 | 1.756 | | 1980 | 1.87 | | 1979 | 1.833 | | 1978 | 1.868 | | 1977 | 1.873 | | 1976 | 1.9 | | 1975 | 1.879 | | 1974 | 1.849 | | 1973 | 1.827 | | 1972 | 1.826 | | 1971 | 1.741 | | 1970 | 1.823 | | 1969 | 1.925 | | 1968 | 1.939 | | 1967 | 1.975 | | 1966 | 1.998 | | 1965 | 2.055 | | 1964 | 1.995 | | 1963 | 2.029 | | 1962 | 2.015 | | 1961 | 2.073 | | 1960 | 2.113 |
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