| Year | Value | | 2021 | 1.493 | | 2020 | 1.505 | | 2019 | 1.504 | | 2018 | 1.579 | | 2017 | 1.621 | | 2016 | 1.762 | | 2015 | 1.777 | | 2014 | 1.75 | | 2013 | 1.707 | | 2012 | 1.691 | | 2011 | 1.582 | | 2010 | 1.567 | | 2009 | 1.542 | | 2008 | 1.502 | | 2007 | 1.416 | | 2006 | 1.305 | | 2005 | 1.294 | | 2004 | 1.344 | | 2003 | 1.319 | | 2002 | 1.286 | | 2001 | 1.223 | | 2000 | 1.195 | | 1999 | 1.157 | | 1998 | 1.232 | | 1997 | 1.218 | | 1996 | 1.27 | | 1995 | 1.337 | | 1994 | 1.4 | | 1993 | 1.385 | | 1992 | 1.552 | | 1991 | 1.732 | | 1990 | 1.892 | | 1989 | 2.01 | | 1988 | 2.12 | | 1987 | 2.22 | | 1986 | 2.15 | | 1985 | 2.05 | | 1984 | 2.06 | | 1983 | 2.11 | | 1982 | 2.04 | | 1981 | 1.91 | | 1980 | 1.89 | | 1979 | 1.9 | | 1978 | 1.92 | | 1977 | 1.95 | | 1976 | 1.97 | | 1975 | 1.98 | | 1974 | 2 | | 1973 | 2.01 | | 1972 | 2.04 | | 1971 | 2.03 | | 1970 | 1.99 | | 1969 | 1.97 | | 1968 | 1.99 | | 1967 | 2.04 | | 1966 | 2.1 | | 1965 | 2.13 | | 1964 | 2.18 | | 1963 | 2.27 | | 1962 | 2.36 | | 1961 | 2.45 | | 1960 | 2.52 |
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