| Year | Value | | 2020 | 0.35112816748697 | | 2019 | 0.34616324914595 | | 2018 | 0.35505268412963 | | 2017 | 0.35722406537161 | | 2016 | 0.33992233756585 | | 2015 | 0.34253620709201 | | 2014 | 0.35825774664757 | | 2013 | 0.33614800581347 | | 2012 | 0.34140027703081 | | 2011 | 0.34375399770988 | | 2010 | 0.34699082898486 | | 2009 | 0.35056256057781 | | 2008 | 0.34446426549239 | | 2007 | 0.34992826197248 | | 2006 | 0.35594642427902 | | 2005 | 0.40099344714582 | | 2004 | 0.40444649617177 | | 2003 | 0.3552139350888 | | 2002 | 0.36359491724999 | | 2001 | 0.40170405168065 | | 2000 | 0.42318110736673 | | 1999 | 0.43925929391345 | | 1998 | 0.44710390125798 | | 1997 | 0.47178265965755 | | 1996 | 0.52601805257043 | | 1995 | 0.50400440487866 | | 1994 | 0.5028027229382 | | 1993 | 0.51433505951398 | | 1992 | 0.55818401230292 | | 1991 | 0.58408326908417 | | 1990 | 0.59356781263234 |
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