| Year | Value | | 2021 | 37.172752109323 | | 2020 | 37.17730548855 | | 2019 | 37.16772156447 | | 2018 | 37.156646781477 | | 2017 | 37.152233917365 | | 2016 | 37.142868581403 | | 2015 | 37.127532467013 | | 2014 | 37.084448531617 | | 2013 | 37.082113512325 | | 2012 | 37.079778493033 | | 2011 | 37.101920460911 | | 2010 | 37.089938201236 | | 2009 | 36.899288092087 | | 2008 | 36.597951082598 | | 2007 | 36.284420268077 | | 2006 | 36.002998116157 | | 2005 | 35.704251738163 | | 2004 | 35.407055571137 | | 2003 | 35.114186414535 | | 2002 | 34.835307790959 | | 2001 | 34.580500280831 | | 2000 | 34.256372745491 | | 1999 | 33.587624139036 | | 1998 | 32.949054941534 | | 1997 | 32.310485744033 | | 1996 | 31.671916546532 | | 1995 | 31.033347349031 | | 1994 | 30.39477815153 | | 1993 | 29.756208954029 | | 1992 | 29.117639756527 | | 1991 | 28.479070559026 | | 1990 | 27.840501361525 |
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