| Year | Value | | 2021 | 28.58784676354 | | 2020 | 28.562635402906 | | 2019 | 28.311955085865 | | 2018 | 28.071334214003 | | 2017 | 27.608982826948 | | 2016 | 28.051519154558 | | 2015 | 27.394319682959 | | 2014 | 26.981505944518 | | 2013 | 26.948480845442 | | 2012 | 26.519154557464 | | 2011 | 27.24570673712 | | 2010 | 27.542932628798 | | 2009 | 27.74108322325 | | 2008 | 27.873183619551 | | 2007 | 27.708058124174 | | 2006 | 27.8071334214 | | 2005 | 27.840158520476 | | 2004 | 27.74108322325 | | 2003 | 27.575957727873 | | 2002 | 27.476882430647 | | 2001 | 27.906208718626 | | 2000 | 28.467635402906 |
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