| Year | Value | | 2022 | 19.138453810442 | | 2021 | 19.116839048634 | | 2020 | 18.750644729344 | | 2019 | 19.826597189919 | | 2018 | 20.141022535478 | | 2017 | 19.9876498649 | | 2016 | 19.713745572241 | | 2015 | 19.700010039843 | | 2014 | 19.777901772831 | | 2013 | 19.751544642443 | | 2012 | 20.477539941353 | | 2011 | 20.305665282136 | | 2010 | 19.685676403117 | | 2009 | 18.946285984022 | | 2008 | 20.302113498036 | | 2007 | 21.394270036889 | | 2006 | 21.689955206642 | | 2005 | 19.886092731864 |
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