| Year | Value | | 2021 | 5.4445192152373 | | 2020 | 8.0112901344609 | | 2019 | 9.3019436141062 | | 2018 | 6.1689089093843 | | 2017 | 5.9818468716613 | | 2016 | 6.3844069893483 | | 2015 | 11.456734933854 | | 2014 | 8.2989008082068 | | 2013 | 8.5163499429095 | | 2012 | 8.7422190526891 | | 2011 | 7.0157901125194 | | 2010 | 7.5861592239033 | | 2009 | 12.763096647524 | | 2008 | 7.786359889133 | | 2007 | 7.5466881535228 | | 2006 | 9.6688828864427 |
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