| Year | Value | | 2023 | 3.129 | | 2022 | 3.171 | | 2021 | 3.198 | | 2020 | 3.234 | | 2019 | 3.274 | | 2018 | 3.326 | | 2017 | 3.388 | | 2016 | 3.463 | | 2015 | 3.54 | | 2014 | 3.619 | | 2013 | 3.696 | | 2012 | 3.768 | | 2011 | 3.829 | | 2010 | 3.879 | | 2009 | 3.946 | | 2008 | 4.012 | | 2007 | 4.086 | | 2006 | 4.141 | | 2005 | 4.195 | | 2004 | 4.186 | | 2003 | 4.175 | | 2002 | 4.138 | | 2001 | 4.127 | | 2000 | 4.159 | | 1999 | 4.228 | | 1998 | 4.309 | | 1997 | 4.378 | | 1996 | 4.455 | | 1995 | 4.563 | | 1994 | 4.658 | | 1993 | 4.726 | | 1992 | 4.787 | | 1991 | 4.852 | | 1990 | 4.929 | | 1989 | 5.006 | | 1988 | 5.103 | | 1987 | 5.192 | | 1986 | 5.273 | | 1985 | 5.344 | | 1984 | 5.407 | | 1983 | 5.45 | | 1982 | 5.497 | | 1981 | 5.554 | | 1980 | 5.599 | | 1979 | 5.647 | | 1978 | 5.684 | | 1977 | 5.699 | | 1976 | 5.726 | | 1975 | 5.746 |
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