| Year | Value | | 2021 | 21.474576022957 | | 2020 | 20.851776853285 | | 2019 | 18.534307279126 | | 2018 | 18.781841913298 | | 2017 | 5.7407220128789 | | 2016 | 5.3138898775539 | | 2015 | 5.0761332194292 | | 2014 | 5.1924093643107 | | 2013 | 4.4359404081746 | | 2012 | 4.2152123132331 | | 2011 | 4.9135802937843 | | 2010 | 5.0174463417538 | | 2009 | 4.6905300744165 | | 2008 | 4.6189425782633 | | 2007 | 4.3865014814402 | | 2006 | 4.2238340598882 | | 2005 | 4.6569467053497 |
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