| Year | Value | | 2021 | 11.74339411573 | | 2020 | 14.743400658762 | | 2019 | 4.8831041451921 | | 2018 | 5.7569243841705 | | 2017 | 9.3801732181231 | | 2016 | 23.113896192986 | | 2015 | 26.96606435904 | | 2014 | 20.82794057013 | | 2013 | 15.193437648672 | | 2012 | 13.444080774041 | | 2011 | 21.641273394107 | | 2010 | 24.265234507868 | | 2009 | 22.751782134221 | | 2008 | 22.218797355588 | | 2007 | 23.366829993357 | | 2006 | 22.52273573628 | | 2005 | 26.213591416103 |
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