| Year | Value | | 2023 | 1.212 | | 2022 | 1.221 | | 2021 | 1.234 | | 2020 | 1.259 | | 2019 | 1.285 | | 2018 | 1.323 | | 2017 | 1.363 | | 2016 | 1.4 | | 2015 | 1.451 | | 2014 | 1.484 | | 2013 | 1.526 | | 2012 | 1.563 | | 2011 | 1.571 | | 2010 | 1.562 | | 2009 | 1.565 | | 2008 | 1.587 | | 2007 | 1.616 | | 2006 | 1.631 | | 2005 | 1.644 | | 2004 | 1.665 | | 2003 | 1.673 | | 2002 | 1.688 | | 2001 | 1.711 | | 2000 | 1.734 | | 1999 | 1.768 | | 1998 | 1.815 | | 1997 | 1.845 | | 1996 | 1.865 | | 1995 | 1.888 | | 1994 | 1.928 | | 1993 | 1.967 | | 1992 | 2.008 | | 1991 | 2.036 | | 1990 | 2.065 | | 1989 | 2.136 | | 1988 | 2.171 | | 1987 | 2.255 | | 1986 | 2.358 | | 1985 | 2.45 | | 1984 | 2.582 | | 1983 | 2.755 | | 1982 | 2.943 | | 1981 | 3.127 | | 1980 | 3.293 | | 1979 | 3.451 | | 1978 | 3.617 | | 1977 | 3.865 | | 1976 | 4.119 | | 1975 | 4.364 |
|