| Year | Value | | 2019 | 19.566098766161 | | 2018 | 20.324413316586 | | 2017 | 19.746033321821 | | 2016 | 21.515321390738 | | 2015 | 22.196224132115 | | 2014 | 21.733735269776 | | 2013 | 21.383780773053 | | 2012 | 21.873947717789 | | 2011 | 22.331177411875 | | 2010 | 22.30155267632 | | 2009 | 22.840662371627 | | 2008 | 24.13803282018 | | 2007 | 22.537141624751 | | 2006 | 24.104049959012 | | 2005 | 22.082570411257 | | 2004 | 20.186017673451 | | 2003 | 19.752176964075 | | 2002 | 18.315299138008 | | 2001 | 19.039092329471 |
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