| Year | Value | | 2021 | 16.725887876305 | | 2020 | 20.184391128685 | | 2019 | 16.844159584182 | | 2018 | 17.107980538727 | | 2017 | 14.786498456037 | | 2016 | 13.450748922461 | | 2015 | 11.859344066447 | | 2014 | 13.389181062337 | | 2013 | 14.390433248044 | | 2012 | 18.063301387101 | | 2011 | 17.495599600683 | | 2010 | 15.838709599888 | | 2009 | 11.49202764266 | | 2008 | 9.6044781547624 | | 2007 | 10.168902614052 | | 2006 | 6.313850630507 | | 2005 | 5.8537000308269 |
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