| Year | Value | | 2022 | 10.240209788913 | | 2021 | 9.8287070388385 | | 2020 | 6.6742459082201 | | 2019 | 10.191584599993 | | 2018 | 9.720664629465 | | 2017 | 9.6738075394896 | | 2016 | 10.569936707347 | | 2015 | 10.684220823146 | | 2014 | 10.815064801703 | | 2013 | 10.480148675246 | | 2012 | 7.8527113547841 | | 2011 | 4.6612751964924 | | 2010 | 7.3699506122792 | | 2009 | 5.9289172812077 | | 2008 | 10.100515300911 | | 2007 | 12.736128614558 | | 2006 | 15.359595888892 |
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