| Year | Value | | 2020 | 0.34749092440578 | | 2019 | 0.35382048280928 | | 2018 | 0.34658887591247 | | 2017 | 0.37239523497953 | | 2016 | 0.3554448028619 | | 2015 | 0.36482978140812 | | 2014 | 0.37444165917112 | | 2013 | 0.38431641886522 | | 2012 | 0.39442930109248 | | 2011 | 0.40488033174066 | | 2010 | 0.41578182631049 | | 2009 | 0.42701665502702 | | 2008 | 0.46088416964508 | | 2007 | 0.47508322483569 | | 2006 | 0.49042859435117 | | 2005 | 0.50586964439699 | | 2004 | 0.46664053479672 | | 2003 | 0.50994893930621 | | 2002 | 0.5803807635895 | | 2001 | 0.59653396392186 | | 2000 | 0.46516010452982 | | 1999 | 0.47609452595729 | | 1998 | 0.49122108688528 | | 1997 | 0.50712261897751 | | 1996 | 0.52836328633835 | | 1995 | 0.54958256385903 | | 1994 | 0.59087817052301 | | 1993 | 0.59456787921354 | | 1992 | 0.59218771166084 | | 1991 | 0.61117829828099 |
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