| Year | Value | | 2021 | 16.364933301679 | | 2020 | 17.885172776263 | | 2019 | 19.732055226281 | | 2018 | 17.052084547774 | | 2017 | 15.788718932731 | | 2016 | 14.825890552391 | | 2015 | 14.582878104904 | | 2014 | 14.626630888905 | | 2013 | 12.07885296033 | | 2012 | 11.082486348965 | | 2011 | 10.154692869106 | | 2010 | 10.003040138155 | | 2009 | 9.6477810502197 | | 2008 | 10.555196360888 | | 2007 | 9.6969792647982 | | 2006 | 8.1788220689691 | | 2005 | 7.8932427686057 | | 2004 | 8.1172650354612 | | 2003 | 7.5378444155731 | | 2002 | 8.1729112738353 |
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