| Year | Value | | 2021 | 3.1264149796684 | | 2020 | 3.1924965009233 | | 2019 | 3.5083208292443 | | 2018 | 3.4818267783112 | | 2017 | 3.8894547100302 | | 2016 | 3.8943413412769 | | 2015 | 4.0372533556766 | | 2014 | 4.637551666075 | | 2013 | 4.5518209520264 | | 2012 | 5.1138015492144 | | 2011 | 5.1448054630867 | | 2010 | 4.8815968468234 | | 2009 | 4.1959027243935 | | 2008 | 5.5509971700799 | | 2007 | 5.4970404709942 | | 2006 | 5.8238700685783 | | 2005 | 6.7280914600204 |
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