| Year | Value | | 2021 | 32.381258175764 | | 2020 | 32.377809489832 | | 2019 | 31.125314429453 | | 2018 | 31.122798993826 | | 2017 | 31.121198262063 | | 2016 | 31.101989480906 | | 2015 | 31.094557512006 | | 2014 | 31.079624971416 | | 2013 | 31.064692430825 | | 2012 | 31.049759890235 | | 2011 | 31.034827349646 | | 2010 | 31.019894809056 | | 2009 | 30.730619711868 | | 2008 | 30.441344614681 | | 2007 | 30.152069517494 | | 2006 | 29.862794420306 |
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