| Year | Value | | 2020 | 0.65043390936403 | | 2019 | 0.63108346042484 | | 2018 | 0.64761247685768 | | 2017 | 0.63759025619259 | | 2016 | 0.63987230689324 | | 2015 | 0.65685523020737 | | 2014 | 0.66213671471239 | | 2013 | 0.66092763290378 | | 2012 | 0.71856300236888 | | 2011 | 0.72328226433587 | | 2010 | 0.72840637536464 | | 2009 | 0.72882765371888 | | 2008 | 0.71644908723854 | | 2007 | 0.70565375140375 | | 2006 | 0.77954960806164 | | 2005 | 0.76129368260225 | | 2004 | 0.76203106081971 | | 2003 | 0.78436168538067 | | 2002 | 0.79755245948315 | | 2001 | 0.820307478062 | | 2000 | 0.8501134382362 | | 1999 | 0.86073520939348 | | 1998 | 0.90836138944217 | | 1997 | 0.91138889313965 | | 1996 | 0.96506478490442 | | 1995 | 0.98156356094307 | | 1994 | 0.72881898754526 | | 1993 | 0.74456405219931 | | 1992 | 0.81928548030334 | | 1991 | 0.71745393083803 |
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