| Year | Value | | 2024 | 1.892 | | 2023 | 1.91 | | 2022 | 1.94 | | 2021 | 1.97 | | 2020 | 1.99 | | 2019 | 2.02 | | 2018 | 2.03 | | 2017 | 2.041 | | 2016 | 2.086 | | 2015 | 2.137 | | 2014 | 2.211 | | 2013 | 2.269 | | 2012 | 2.294 | | 2011 | 2.317 | | 2010 | 2.34 | | 2009 | 2.364 | | 2008 | 2.391 | | 2007 | 2.421 | | 2006 | 2.456 | | 2005 | 2.495 | | 2004 | 2.536 | | 2003 | 2.579 | | 2002 | 2.633 | | 2001 | 2.671 | | 2000 | 2.714 | | 1999 | 2.763 | | 1998 | 2.815 | | 1997 | 2.886 | | 1996 | 2.964 | | 1995 | 3.044 | | 1994 | 3.132 | | 1993 | 3.211 | | 1992 | 3.285 | | 1991 | 3.363 | | 1990 | 3.444 | | 1989 | 3.532 | | 1988 | 3.64 | | 1987 | 3.803 | | 1986 | 3.971 | | 1985 | 4.087 | | 1984 | 4.184 | | 1983 | 4.296 | | 1982 | 4.425 | | 1981 | 4.574 | | 1980 | 4.739 | | 1979 | 4.964 | | 1978 | 5.202 | | 1977 | 5.361 | | 1976 | 5.543 |
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