| Year | Value | | 2022 | 28.457254565881 | | 2021 | 29.550450386397 | | 2020 | 28.16766715193 | | 2019 | 29.171701898643 | | 2018 | 29.125467458636 | | 2017 | 29.289667171355 | | 2016 | 28.727223241372 | | 2015 | 28.178915820504 | | 2014 | 25.772088625781 | | 2013 | 25.252523131586 | | 2012 | 24.895748835138 | | 2011 | 25.580571408527 | | 2010 | 26.377322723446 | | 2009 | 25.331115503121 | | 2008 | 28.642107407024 | | 2007 | 30.343379938353 | | 2006 | 29.815932177797 | | 2005 | 29.514876978897 | | 2004 | 29.315884376403 | | 2003 | 28.715876806283 | | 2002 | 28.504410929852 | | 2001 | 29.722942026636 | | 2000 | 31.0308542274 | | 1999 | 30.651830649459 | | 1998 | 32.354470968369 | | 1997 | 33.210080234917 | | 1996 | 33.427340662551 |
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