| Year | Value | | 2021 | 9.1395145093635 | | 2020 | 8.7595321107001 | | 2019 | 10.233543508886 | | 2018 | 10.85118249939 | | 2017 | 10.120126713415 | | 2016 | 8.4089725652163 | | 2015 | 9.2025029569386 | | 2014 | 10.181563394653 | | 2013 | 10.986269067857 | | 2012 | 11.79294552841 | | 2011 | 12.857321949553 | | 2010 | 13.32172882839 | | 2009 | 10.571086804788 | | 2008 | 12.21194155918 | | 2007 | 11.891859177149 | | 2006 | 14.53368777493 | | 2005 | 14.823529411765 |
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