| Year | Value | | 2021 | 0.82222764775851 | | 2020 | 0.81830895970637 | | 2019 | 0.81411035036975 | | 2018 | 0.8103316019668 | | 2017 | 0.8157897941044 | | 2016 | 0.821247986242 | | 2015 | 0.821247986242 | | 2014 | 0.81805738661651 | | 2013 | 0.81486644218093 | | 2012 | 0.81167549774535 | | 2011 | 0.80848455330976 | | 2010 | 0.80529360887418 | | 2009 | 0.79106031724705 | | 2008 | 0.77682702561993 | | 2007 | 0.76259373399279 | | 2006 | 0.74836044236567 | | 2005 | 0.73412715073854 | | 2004 | 0.71989385911141 | | 2003 | 0.70566056748428 | | 2002 | 0.69142727585715 | | 2001 | 0.67719398423002 | | 2000 | 0.66296069260289 | | 1999 | 0.6666554703704 | | 1998 | 0.67035024813792 | | 1997 | 0.67404502590543 | | 1996 | 0.67773980367294 | | 1995 | 0.68143458144046 | | 1994 | 0.68512935920797 | | 1993 | 0.68882413697549 | | 1992 | 0.692518914743 | | 1991 | 0.69621369251052 | | 1990 | 0.69990847027803 |
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