| Year | Value | | 2022 | 7.037 | | 2021 | 7.94 | | 2020 | 10.679 | | 2019 | 5.551 | | 2018 | 5.622 | | 2017 | 5.528 | | 2016 | 6.727 | | 2015 | 6.147 | | 2014 | 7.078 | | 2013 | 5.646 | | 2012 | 3.755 | | 2011 | 4.475 | | 2010 | 4.119 | | 2009 | 3.292 | | 2008 | 3.156 | | 2007 | 3.211 | | 2006 | 3.575 | | 2005 | 4.909 | | 2004 | 5.99 | | 2003 | 5.3 | | 2002 | 4.02 | | 2001 | 4 | | 1999 | 3.85 | | 1998 | 4.02 | | 1997 | 3.32 | | 1996 | 4.37 | | 1995 | 3.24 | | 1992 | 3.06 | | 1991 | 4.58 | | 1990 | 4.78 | | 1987 | 11.4 | | 1986 | 12.12 | | 1982 | 7.3 | | 1974 | 8.1 |
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