| Year | Value | | 2021 | 0.29821160376443 | | 2020 | 0.30348306975842 | | 2019 | 0.30881924905404 | | 2018 | 0.31405840690793 | | 2017 | 0.31939458620355 | | 2016 | 0.32463374405744 | | 2015 | 0.32991171048802 | | 2014 | 0.3351896769186 | | 2013 | 0.34046764334918 | | 2012 | 0.34574560977976 | | 2011 | 0.35102357621034 | | 2010 | 0.35630154264092 | | 2009 | 0.3615795090715 | | 2008 | 0.36685747550209 | | 2007 | 0.37213544193267 | | 2006 | 0.37741340836325 | | 2005 | 0.38269137479383 | | 2004 | 0.38796934122441 | | 2003 | 0.39324730765499 | | 2002 | 0.39852527408557 | | 2001 | 0.40380324051615 | | 2000 | 0.40908120694673 | | 1999 | 0.41435917337732 | | 1998 | 0.4196371398079 | | 1997 | 0.42491510623848 | | 1996 | 0.43019307266906 | | 1995 | 0.43547103909964 | | 1994 | 0.44074900553022 | | 1993 | 0.4460269719608 | | 1992 | 0.45130493839139 | | 1991 | 0.45658290482197 | | 1990 | 0.46186087125255 |
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