| Year | Value | | 2022 | 18.528232124746 | | 2021 | 20.294627609188 | | 2020 | 21.54430854682 | | 2019 | 18.005573741164 | | 2018 | 20.431529603733 | | 2017 | 21.684712568524 | | 2016 | 19.571566856963 | | 2015 | 17.807041385372 | | 2014 | 24.125478974654 | | 2013 | 22.391669269829 | | 2012 | 25.447702263471 | | 2011 | 18.604991253005 | | 2010 | 17.935418913713 | | 2009 | 11.804585363974 | | 2008 | 29.87919230162 | | 2007 | 36.854455317895 | | 2006 | 28.904589242378 | | 2005 | 36.08228263826 | | 2004 | 33.147885519918 | | 2003 | 23.885790319218 | | 2002 | 27.385740558445 | | 2001 | 30.461156006356 | | 2000 | 31.737206518745 | | 1999 | 33.251094492918 |
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