| Year | Value | | 2021 | 4.13 | | 2020 | 3.96 | | 2019 | 5.41 | | 2018 | 4.67 | | 2017 | 4.8 | | 2016 | 3.93 | | 2015 | 3.67 | | 2014 | 3.71 | | 2013 | 3.68 | | 2012 | 4.53 | | 2011 | 3.8 | | 2010 | 3.07 | | 2009 | 3.48 | | 2008 | 3.5 | | 2007 | 3.83 | | 2006 | 5.88 | | 2005 | 4.72 | | 2004 | 4.15 | | 2003 | 5.1 | | 2002 | 4.52 | | 2001 | 5.02 | | 2000 | 4.43 | | 1999 | 4.33 | | 1998 | 4.53 | | 1997 | 4.93 | | 1996 | 5.94 | | 1995 | 11.92 | | 1993 | 6.72 | | 1990 | 6.06 |
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