| Year | Value | | 2020 | 0.69936894024205 | | 2019 | 0.71504145648965 | | 2018 | 0.72130092647713 | | 2017 | 0.73553129430231 | | 2016 | 0.74569880705499 | | 2015 | 0.72076653646554 | | 2014 | 0.71568311629637 | | 2013 | 0.73321792337472 | | 2012 | 0.7436227030069 | | 2011 | 0.73876514392189 | | 2010 | 0.73758763021617 | | 2009 | 0.74081646853353 | | 2008 | 0.71508463740566 | | 2007 | 0.72110012423505 | | 2006 | 0.73761423802749 | | 2005 | 0.83691531748593 | | 2004 | 0.7765035602512 | | 2003 | 0.7515402687061 | | 2002 | 0.75817274325581 | | 2001 | 0.73952246141739 | | 2000 | 0.81652275883112 | | 1999 | 0.82187553193483 | | 1998 | 0.84626809479784 | | 1997 | 0.87264361593775 | | 1996 | 0.89598643765485 | | 1995 | 0.90295048348491 | | 1994 | 0.52181015691961 | | 1993 | 0.53388060395392 | | 1992 | 0.54699995156814 | | 1991 | 0.5552803780703 |
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