| Year | Value | | 2021 | 17.295973161232 | | 2020 | 16.136261143265 | | 2019 | 16.912734333579 | | 2018 | 17.956816764573 | | 2017 | 16.468847002984 | | 2016 | 16.689519362292 | | 2015 | 17.89022288149 | | 2014 | 18.345583125397 | | 2013 | 17.066239636076 | | 2012 | 18.016257405925 | | 2011 | 16.153035564083 | | 2010 | 15.592022952784 | | 2009 | 16.939109189865 | | 2008 | 17.670915317626 | | 2007 | 17.638263077019 | | 2006 | 17.222501059829 | | 2005 | 16.935093888579 | | 2004 | 15.925098381436 | | 2003 | 16.905495491106 | | 2002 | 18.098258600823 |
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