| Year | Value | | 2020 | 0.41278505387877 | | 2019 | 0.40343375920249 | | 2018 | 0.41220886449967 | | 2017 | 0.2785203051747 | | 2016 | 0.28043341516783 | | 2015 | 0.24478935698448 | | 2014 | 0.25907650116059 | | 2013 | 0.21784446367155 | | 2012 | 0.22517289777628 | | 2011 | 0.22835103121066 | | 2010 | 0.23323855441546 | | 2009 | 0.23042150036151 | | 2008 | 0.23938774191129 | | 2007 | 0.24185064110574 | | 2006 | 0.24433349893715 | | 2005 | 0.24680246835375 | | 2004 | 0.16628683981007 | | 2003 | 0.25271713034644 | | 2002 | 0.25484308037326 | | 2001 | 0.25700202003588 | | 2000 | 0.25842753734924 | | 1999 | 0.26168619492675 | | 1998 | 0.30171735431269 | | 1997 | 0.30385528432361 | | 1996 | 0.30872909462988 | | 1995 | 0.31098478218182 | | 1994 | 0.26844004123239 | | 1993 | 0.27028634135003 | | 1992 | 0.27211550759066 | | 1991 | 0.2742115048179 |
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