| Year | Value | | 2024 | 45.68 | | 2023 | 46.392 | | 2022 | 47.111 | | 2021 | 47.837 | | 2020 | 48.57 | | 2019 | 49.308 | | 2018 | 50.051 | | 2017 | 50.8 | | 2016 | 51.552 | | 2015 | 52.306 | | 2014 | 53.057 | | 2013 | 53.807 | | 2012 | 54.555 | | 2011 | 55.302 | | 2010 | 56.144 | | 2009 | 57.457 | | 2008 | 58.758 | | 2007 | 60.05 | | 2006 | 61.327 | | 2005 | 62.589 | | 2004 | 63.831 | | 2003 | 65.059 | | 2002 | 66.266 | | 2001 | 67.452 | | 2000 | 68.614 | | 1999 | 69.031 | | 1998 | 69.205 | | 1997 | 69.378 | | 1996 | 69.551 | | 1995 | 69.724 | | 1994 | 69.895 | | 1993 | 70.066 | | 1992 | 70.237 | | 1991 | 70.407 | | 1990 | 70.576 | | 1989 | 70.833 | | 1988 | 71.103 | | 1987 | 71.372 | | 1986 | 71.639 | | 1985 | 71.905 | | 1984 | 72.168 | | 1983 | 72.431 | | 1982 | 72.692 | | 1981 | 72.951 | | 1980 | 73.209 | | 1979 | 73.758 | | 1978 | 74.394 | | 1977 | 75.02 | | 1976 | 75.635 | | 1975 | 76.242 |
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