| Year | Value | | 2022 | 3.574 | | 2021 | 3.9 | | 2020 | 4.049 | | 2019 | 4.165 | | 2018 | 4.763 | | 2017 | 5.648 | | 2016 | 5.844 | | 2015 | 1 | | 2014 | 0.5 | | 2013 | 0.5 | | 2012 | 0.5 | | 2011 | 0.6 | | 2009 | 6.1 | | 2008 | 0.8 | | 2007 | 1 | | 2006 | 1.2 | | 2005 | 1.5 | | 2004 | 1.9 | | 2003 | 3.1 | | 2002 | 3 | | 2001 | 2.3 | | 2000 | 2.1 | | 1999 | 2.1 | | 1998 | 2.3 | | 1997 | 2.8 | | 1996 | 4 | | 1995 | 2.9 | | 1994 | 2.1 | | 1993 | 1.4 | | 1992 | 0.5 | | 1991 | 0.05 |
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