| Year | Value | | 2020 | 23.631296944072 | | 2019 | 7.75615987262 | | 2018 | 6.0255610923628 | | 2017 | 15.375170688997 | | 2016 | 25.343259583287 | | 2015 | 25.087533999207 | | 2014 | 9.4793724740067 | | 2013 | 23.304884007567 | | 2012 | 27.384078203653 | | 2011 | 30.261727007522 | | 2010 | 35.772107846792 | | 2009 | 37.349411866681 | | 2008 | 36.287159226513 |
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