| Year | Value | | 2020 | 0.41304609162842 | | 2019 | 0.42207916258486 | | 2018 | 0.43550972057696 | | 2017 | 0.44832532091227 | | 2016 | 0.46462496096112 | | 2015 | 0.48094065328471 | | 2014 | 0.49699986080302 | | 2013 | 0.51406052213539 | | 2012 | 0.53160025972979 | | 2011 | 0.54162480421322 | | 2010 | 0.65462082015343 | | 2009 | 0.66696082855159 | | 2008 | 0.64457598063164 | | 2007 | 0.62175883748663 | | 2005 | 0.29402474322254 | | 2004 | 0.29879120284001 | | 2003 | 0.47031257656706 | | 2002 | 0.40301810056282 | | 2001 | 0.41577741463372 | | 2000 | 0.48921494324685 | | 1999 | 0.50287023062906 | | 1998 | 0.48356528348098 | | 1997 | 0.43559338794128 | | 1996 | 0.36958250801756 | | 1995 | 0.3725056284971 | | 1994 | 0.23929770908338 | | 1993 | 0.25305766412339 | | 1992 | 0.29367646055909 | | 1991 | 0.40274373194827 |
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