Year | Value | 2021 | 18.840910163925 | 2020 | 19.966852537525 | 2019 | 20.869136343185 | 2018 | 19.656275541172 | 2017 | 20.208500366258 | 2016 | 19.694583650088 | 2015 | 18.891137371998 | 2014 | 20.190696624406 | 2013 | 17.151318921111 | 2012 | 16.655769800137 | 2011 | 18.604135782688 | 2010 | 17.639473933028 | 2009 | 15.388168349136 | 2008 | 16.707901224753 | 2007 | 16.728856141321 | 2006 | 17.465446780668 | 2005 | 16.686182168491 |
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