| Year | Value | | 2021 | 23.808854308673 | | 2020 | 24.442437408471 | | 2019 | 30.790193834506 | | 2018 | 31.906397509416 | | 2017 | 32.905737146174 | | 2016 | 31.169560999378 | | 2015 | 23.399812982757 | | 2014 | 30.022522035251 | | 2013 | 25.021147414105 | | 2012 | 48.686732356686 | | 2011 | 40.59468589961 | | 2010 | 34.615229366486 | | 2009 | 30.888151265038 | | 2008 | 34.624430987657 | | 2007 | 26.789459855937 | | 2006 | 51.826305881143 |
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