| Year | Value | | 2020 | 0.49666849687048 | | 2019 | 0.49632188771008 | | 2018 | 0.50664795241886 | | 2017 | 0.52096118540926 | | 2016 | 0.53047062120591 | | 2015 | 0.53550836244864 | | 2014 | 0.54346946326225 | | 2013 | 0.55016473184479 | | 2012 | 0.55295981858014 | | 2011 | 0.56572846558986 | | 2010 | 0.4966568805065 | | 2009 | 0.50838269784652 | | 2008 | 0.51379264435911 | | 2007 | 0.5230158094469 | | 2006 | 0.54829716564563 | | 2005 | 0.55581274893869 | | 2004 | 0.55420671079955 | | 2003 | 0.48155084253037 | | 2002 | 0.48319900842849 | | 2001 | 0.48388165615853 | | 2000 | 0.48881788356521 | | 1999 | 0.51026736680667 | | 1998 | 0.52388371142234 | | 1997 | 0.5244985127758 | | 1996 | 0.53398268797751 | | 1995 | 0.51932145334855 | | 1994 | 0.3237388769392 | | 1993 | 0.32693434353713 | | 1992 | 0.34645620900638 | | 1991 | 0.35104009011679 |
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