| Year | Value | | 2023 | 1.26 | | 2022 | 1.33 | | 2021 | 1.44 | | 2020 | 1.41 | | 2019 | 1.47 | | 2018 | 1.51 | | 2017 | 1.55 | | 2016 | 1.59 | | 2015 | 1.6 | | 2014 | 1.61 | | 2013 | 1.61 | | 2012 | 1.63 | | 2011 | 1.63 | | 2010 | 1.65 | | 2009 | 1.69 | | 2008 | 1.7 | | 2007 | 1.67 | | 2006 | 1.63 | | 2005 | 1.58 | | 2004 | 1.56 | | 2003 | 1.55 | | 2002 | 1.52 | | 2001 | 1.54 | | 2000 | 1.51 | | 1999 | 1.55 | | 1998 | 1.56 | | 1997 | 1.57 | | 1996 | 1.63 | | 1995 | 1.67 | | 1994 | 1.69 | | 1993 | 1.69 | | 1992 | 1.71 | | 1991 | 1.72 | | 1990 | 1.83 | | 1989 | 1.77 | | 1988 | 1.68 | | 1987 | 1.68 | | 1986 | 1.675 | | 1985 | 1.67 | | 1984 | 1.65 | | 1983 | 1.68 | | 1982 | 1.69 | | 1981 | 1.7 | | 1980 | 1.74 | | 1979 | 1.754 | | 1978 | 1.768 | | 1977 | 1.782 | | 1976 | 1.796 |
|