| Year | Value | | 2020 | 0.62942791091928 | | 2019 | 0.62887388737857 | | 2018 | 0.6439295400741 | | 2017 | 0.65077734712915 | | 2016 | 0.65812334215286 | | 2015 | 0.66446069420265 | | 2014 | 0.67943718878132 | | 2013 | 0.68562554007882 | | 2012 | 0.68770261746295 | | 2011 | 0.68930006710555 | | 2010 | 0.6836756470329 | | 2009 | 0.68378885463114 | | 2008 | 0.67507758196689 | | 2007 | 0.67836303108865 | | 2006 | 0.74735678813065 | | 2005 | 0.76687835275769 | | 2004 | 0.75601072841565 | | 2003 | 0.78319715307071 | | 2002 | 0.78576944431008 | | 2001 | 0.78857083424936 | | 2000 | 0.81763337872538 | | 1999 | 0.82049113802123 | | 1998 | 0.83415379527541 | | 1997 | 0.82578488568841 | | 1996 | 0.87570200591374 | | 1995 | 0.89097248837811 | | 1994 | 0.70972125654173 | | 1993 | 0.75244395374374 | | 1992 | 0.78669097855286 | | 1991 | 0.82323180154371 |
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