| Year | Value | | 2021 | 6.6586743657589 | | 2020 | 6.1782810873992 | | 2019 | 4.9840199305553 | | 2018 | 4.6163356172272 | | 2017 | 4.6591136214249 | | 2016 | 4.5195182097729 | | 2015 | 4.4225811002725 | | 2014 | 4.6942574065859 | | 2013 | 5.149765190308 | | 2012 | 5.3082214130023 | | 2011 | 4.7890001267267 | | 2010 | 6.388892655214 | | 2009 | 7.3624037283697 | | 2008 | 8.1648320191532 | | 2007 | 7.1748647142112 | | 2006 | 8.913985693272 | | 2005 | 9.0668397456131 |
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