| Year | Value | | 2024 | 29.891 | | 2023 | 30.41 | | 2022 | 30.882 | | 2021 | 30.932 | | 2020 | 30.988 | | 2019 | 31.121 | | 2018 | 31.327 | | 2017 | 31.813 | | 2016 | 32.704 | | 2015 | 33.918 | | 2014 | 35.407 | | 2013 | 36.975 | | 2012 | 37.805 | | 2011 | 38.142 | | 2010 | 37.869 | | 2009 | 37.518 | | 2008 | 36.361 | | 2007 | 35.651 | | 2006 | 35.203 | | 2005 | 35.803 | | 2004 | 36.326 | | 2003 | 36.613 | | 2002 | 36.539 | | 2001 | 36.463 | | 2000 | 36.128 | | 1999 | 35.615 | | 1998 | 34.47 | | 1997 | 33.372 | | 1996 | 32.405 | | 1995 | 31.665 | | 1994 | 32.025 | | 1993 | 32.379 | | 1992 | 34.269 | | 1991 | 34.913 | | 1990 | 35.51 | | 1989 | 36.387 | | 1988 | 37.653 | | 1987 | 39.499 | | 1986 | 40.936 | | 1985 | 42.336 | | 1984 | 43.721 | | 1983 | 44.988 | | 1982 | 45.723 | | 1981 | 46.313 | | 1980 | 44.84 | | 1979 | 46.305 | | 1978 | 46.766 | | 1977 | 46.51 | | 1976 | 46.524 |
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