| Year | Value | | 2020 | 32.318271119843 | | 2019 | 24.889376465802 | | 2018 | 24.670642462947 | | 2017 | 24.722106733503 | | 2016 | 26.079173611089 | | 2015 | 24.991234936901 | | 2014 | 23.482022526465 | | 2013 | 21.463503206589 | | 2012 | 22.653155966467 | | 2011 | 19.557807347133 | | 2010 | 22.585825592682 | | 2009 | 22.995345191485 | | 2008 | 24.054767975128 |
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