| Year | Value | | 2020 | 0.39725401299731 | | 2019 | 0.40606594126192 | | 2018 | 0.42188522816506 | | 2017 | 0.47628895698985 | | 2016 | 0.44121519203535 | | 2015 | 0.50087154341412 | | 2014 | 0.5100252873828 | | 2013 | 0.51877418680054 | | 2012 | 0.52727320661201 | | 2011 | 0.53592513644481 | | 2010 | 0.54529299687994 | | 2009 | 0.55421516049321 | | 2008 | 0.57489871192431 | | 2007 | 0.58458408688273 | | 2006 | 0.59456883276437 | | 2005 | 0.61062696605814 | | 2004 | 0.59374098049726 | | 2003 | 0.62954793381353 | | 2002 | 0.52794367674564 | | 2001 | 0.55611464089432 | | 2000 | 0.56346211613686 | | 1999 | 0.63782162155267 | | 1998 | 0.65388161434909 | | 1997 | 0.68427508252712 | | 1996 | 0.70435819609818 | | 1995 | 0.72429712999344 | | 1994 | 0.5991804068007 | | 1993 | 0.79370258729406 | | 1992 | 0.81890878584489 | | 1991 | 0.84536252902411 |
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