Year | Value | 2020 | 18.385703293431 | 2019 | 18.224033237213 | 2018 | 18.931606338825 | 2017 | 17.803638365855 | 2016 | 16.72527813244 | 2015 | 17.135596778933 | 2014 | 15.532558902002 | 2013 | 16.270355462073 | 2012 | 16.281082726842 | 2011 | 17.987083017097 | 2010 | 16.822432848252 | 2009 | 16.883593640579 | 2008 | 19.419446372105 | 2007 | 19.175765528895 | 2006 | 22.741766341426 | 2005 | 21.076799897895 |
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