| Year | Value | | 2020 | 0.32467037839833 | | 2019 | 0.33134619075498 | | 2018 | 0.32917023699739 | | 2017 | 0.34253027111271 | | 2016 | 0.32955444239388 | | 2015 | 0.33532410437794 | | 2014 | 0.34118322898582 | | 2013 | 0.34694436507348 | | 2012 | 0.3527795153842 | | 2011 | 0.35891942492354 | | 2010 | 0.5730357862333 | | 2009 | 0.58288434125009 | | 2008 | 0.58377851566017 | | 2007 | 0.59392093786993 | | 2005 | 0.41749791572194 | | 2004 | 0.35681731926392 | | 2003 | 0.40402275272198 | | 2002 | 0.64298033712825 | | 2001 | 0.58347228742722 | | 2000 | 0.65559136209126 | | 1999 | 0.66606387310966 | | 1998 | 0.67982521799318 | | 1997 | 0.68924091362633 | | 1996 | 0.70028519386652 | | 1995 | 0.72046351561558 | | 1994 | 0.46008265384876 | | 1993 | 0.59186797082801 | | 1992 | 0.60962351683679 | | 1991 | 0.62899833273509 |
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