| Year | Value | | 2024 | 1.051 | | 2023 | 0.93 | | 2022 | 0.932 | | 2021 | 1.053 | | 2020 | 1.053 | | 2019 | 0.841 | | 2018 | 0.877 | | 2017 | 0.901 | | 2016 | 0.92 | | 2015 | 0.97 | | 2014 | 1.047 | | 2013 | 1.104 | | 2012 | 1.132 | | 2011 | 1.148 | | 2010 | 1.188 | | 2009 | 1.287 | | 2008 | 1.371 | | 2007 | 1.391 | | 2006 | 1.461 | | 2005 | 1.634 | | 2004 | 1.722 | | 2003 | 1.758 | | 2002 | 1.798 | | 2001 | 1.831 | | 2000 | 1.854 | | 1999 | 1.877 | | 1998 | 1.901 | | 1997 | 1.931 | | 1996 | 1.982 | | 1995 | 2.007 | | 1994 | 2.032 | | 1993 | 2.06 | | 1992 | 2.094 | | 1991 | 2.137 | | 1990 | 2.197 | | 1989 | 2.262 | | 1988 | 2.329 | | 1987 | 2.396 | | 1986 | 2.473 | | 1985 | 2.595 | | 1984 | 2.74 | | 1983 | 2.894 | | 1982 | 3.053 | | 1981 | 3.218 | | 1980 | 3.39 | | 1979 | 3.57 | | 1978 | 3.763 | | 1977 | 3.976 | | 1976 | 4.213 |
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