| Year | Value | | 2020 | 12.298704208642 | | 2019 | 11.918837596449 | | 2018 | 13.180433413254 | | 2017 | 11.42474066756 | | 2016 | 10.713448464484 | | 2015 | 11.354839478577 | | 2014 | 14.938684503902 | | 2013 | 13.111238589959 | | 2012 | 12.089233024944 | | 2011 | 14.585817301434 | | 2010 | 13.873103630324 | | 2009 | 14.426534378144 | | 2008 | 12.379049181212 | | 2007 | 17.010005885815 | | 2006 | 12.379419213996 | | 2005 | 17.420748937071 | | 2004 | 17.169611588303 | | 2003 | 16.724714523154 | | 2002 | 16.028213308609 | | 2001 | 14.950543798408 | | 2000 | 16.080171802178 |
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