| Year | Value | | 2023 | 1.729 | | 2022 | 1.739 | | 2021 | 1.605 | | 2020 | 1.675 | | 2019 | 1.731 | | 2018 | 1.756 | | 2017 | 1.834 | | 2016 | 1.856 | | 2015 | 1.976 | | 2014 | 2.03 | | 2013 | 2.032 | | 2012 | 2.04 | | 2011 | 2.07 | | 2010 | 2.137 | | 2009 | 2.254 | | 2008 | 2.369 | | 2007 | 2.438 | | 2006 | 2.509 | | 2005 | 2.635 | | 2004 | 2.794 | | 2003 | 2.925 | | 2002 | 3.011 | | 2001 | 3.08 | | 2000 | 3.073 | | 1999 | 3.117 | | 1998 | 3.211 | | 1997 | 3.327 | | 1996 | 3.444 | | 1995 | 3.557 | | 1994 | 3.665 | | 1993 | 3.765 | | 1992 | 3.852 | | 1991 | 3.988 | | 1990 | 4.23 | | 1989 | 4.412 | | 1988 | 4.515 | | 1987 | 4.539 | | 1986 | 4.565 | | 1985 | 4.642 | | 1984 | 4.756 | | 1983 | 4.898 | | 1982 | 5.044 | | 1981 | 5.196 | | 1980 | 5.329 | | 1979 | 5.461 | | 1978 | 5.577 | | 1977 | 5.691 | | 1976 | 5.782 |
|