| Year | Value | | 2020 | 0.53074751768613 | | 2019 | 0.49981858526398 | | 2018 | 0.52330477110689 | | 2017 | 0.53624204638136 | | 2016 | 0.54343689280461 | | 2015 | 0.54837687724824 | | 2014 | 0.55460129836022 | | 2013 | 0.55710509105992 | | 2012 | 0.55401512039197 | | 2011 | 0.55910006482024 | | 2010 | 0.57154228829559 | | 2009 | 0.56940606428919 | | 2008 | 0.59555034835521 | | 2007 | 0.59696236537243 | | 2006 | 0.59852468698977 | | 2005 | 0.5813322253825 | | 2004 | 0.58536081468452 | | 2003 | 0.60524563917862 | | 2002 | 0.61303668906343 | | 2001 | 0.60836405081335 | | 2000 | 0.6166943686822 | | 1999 | 0.61997557147561 | | 1998 | 0.63923331249366 | | 1997 | 0.65178572656788 | | 1996 | 0.66630098286784 | | 1995 | 0.64796480176257 | | 1994 | 0.45795173454197 | | 1993 | 0.44225069953855 | | 1992 | 0.45532600431257 | | 1991 | 0.50476479943351 |
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