| Year | Value | | 2020 | 0.64392490090827 | | 2019 | 0.57935651013725 | | 2018 | 0.63108839354092 | | 2017 | 0.62090826534973 | | 2016 | 0.62814834708758 | | 2015 | 0.63644946161356 | | 2014 | 0.64739859716112 | | 2013 | 0.63180199051891 | | 2012 | 0.64957233910399 | | 2011 | 0.66937420667231 | | 2010 | 0.68842866277043 | | 2009 | 0.70078375613038 | | 2008 | 0.65706686943678 | | 2007 | 0.62643391215316 | | 2006 | 0.62680383791094 | | 2005 | 0.4720762719748 | | 2004 | 0.48552830274828 | | 2003 | 0.50221046531697 | | 2002 | 0.5157731685282 | | 2001 | 0.52246550394592 | | 2000 | 0.53850356183308 | | 1999 | 0.51225342335021 | | 1998 | 0.5071496083337 | | 1997 | 0.51629905856671 | | 1996 | 0.54032926641714 | | 1995 | 0.55111433861293 | | 1994 | 0.52363075270843 | | 1993 | 0.53735584201296 | | 1992 | 0.55718744259974 | | 1991 | 0.57813006638089 | | 1990 | 0.59634089994521 |
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