| Year | Value | | 2021 | 7.9651280461438 | | 2020 | 8.0906262160763 | | 2019 | 8.4928637699159 | | 2018 | 9.0526857315335 | | 2017 | 9.419317652533 | | 2016 | 9.1229155606249 | | 2015 | 9.3769204471204 | | 2014 | 9.6786188270568 | | 2013 | 9.9077325831122 | | 2012 | 10.256768682921 | | 2011 | 10.312794889189 | | 2010 | 10.212048608744 | | 2009 | 10.309441736144 | | 2008 | 10.101426526569 | | 2007 | 9.7714060646018 | | 2006 | 9.057253982604 | | 2005 | 8.5692438577418 |
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