| Year | Value | | 2021 | 2.7016275049379 | | 2020 | 2.1813976150463 | | 2019 | 2.4925730470607 | | 2018 | 2.9001935466668 | | 2017 | 2.9005795272447 | | 2016 | 3.7277986662098 | | 2015 | 1.504175363562 | | 2014 | 3.665002420725 | | 2013 | 3.4012358684732 | | 2012 | 1.4840318771164 | | 2011 | 1.9655761215841 | | 2010 | 1.9995852228284 | | 2009 | 1.0383599125057 | | 2008 | 0.89234629716221 | | 2007 | 1.3663629364535 | | 2006 | 2.003133634408 |
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