| Year | Value | | 2020 | 0.43148202288033 | | 2019 | 0.43310836698814 | | 2018 | 0.44482757694652 | | 2017 | 0.44591802830274 | | 2016 | 0.45253443933875 | | 2015 | 0.45415692105574 | | 2014 | 0.46390657386616 | | 2013 | 0.47822143154315 | | 2012 | 0.48037064644687 | | 2011 | 0.48647022931398 | | 2010 | 0.48699157827175 | | 2009 | 0.48577923629654 | | 2008 | 0.53226499820842 | | 2007 | 0.47262629208535 | | 2006 | 0.54061899699898 | | 2005 | 0.70945953136414 | | 2004 | 0.61493222518679 | | 2003 | 0.69968028465657 | | 2002 | 0.61994805327522 | | 2001 | 0.66316667334604 | | 2000 | 0.69316650721409 | | 1999 | 0.74552702423634 | | 1998 | 0.76944374078785 | | 1997 | 0.78347526950003 | | 1996 | 0.88157197367708 | | 1995 | 1.0447797979235 | | 1994 | 1.0418365006741 | | 1993 | 1.1851837151899 | | 1992 | 1.2508526645664 | | 1991 | 1.4643564378741 |
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