| Year | Value | | 2021 | 3.04 | | 2020 | 3.26 | | 2019 | 3.19 | | 2018 | 3.33 | | 2017 | 3.48 | | 2016 | 3.57 | | 2015 | 3.79 | | 2014 | 3.86 | | 2013 | 3.92 | | 2012 | 4.3 | | 2011 | 4.39 | | 2010 | 4.15 | | 2009 | 4.31 | | 2008 | 5.58 | | 2007 | 5.39 | | 2006 | 5.73 | | 2005 | 6.72 | | 2004 | 5.27 | | 2003 | 4.59 | | 2002 | 4.31 | | 2001 | 4.26 | | 2000 | 3.04 | | 1999 | 9.05 | | 1998 | 4.9 | | 1997 | 6.63 | | 1996 | 9.14 | | 1995 | 7.68 |
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