| Year | Value | | 2022 | 4.585 | | 2021 | 5.247 | | 2020 | 6.773 | | 2019 | 5.595 | | 2018 | 5.585 | | 2017 | 5.522 | | 2016 | 6.291 | | 2015 | 6.669 | | 2014 | 5.852 | | 2013 | 5.848 | | 2012 | 5.14 | | 2011 | 4.902 | | 2010 | 4.361 | | 2009 | 5.122 | | 2008 | 5.06 | | 2007 | 4.065 | | 2006 | 4.731 | | 2005 | 4.488 | | 2004 | 5.113 | | 2003 | 3.675 | | 2002 | 2.621 | | 2001 | 1.805 | | 2000 | 2.345 | | 1999 | 2.39 | | 1998 | 2.763 | | 1997 | 2.527 | | 1996 | 3.286 | | 1995 | 2.918 | | 1994 | 3.48 | | 1993 | 2.33 | | 1992 | 2.029 | | 1991 | 1.482 | | 1990 | 1.607 | | 1989 | 1.588 | | 1988 | 1.998 | | 1987 | 2.465 | | 1986 | 2.631 | | 1985 | 2.956 | | 1984 | 2.628 | | 1983 | 3.198 |
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