| Year | Value | | 2021 | 11.541599301793 | | 2020 | 11.479709354134 | | 2019 | 13.120805283798 | | 2018 | 13.568310169013 | | 2017 | 13.542015604973 | | 2016 | 16.248632749118 | | 2015 | 16.893731134307 | | 2014 | 16.808420924845 | | 2013 | 17.213673894862 | | 2012 | 18.507499020333 | | 2011 | 19.256489043663 | | 2010 | 22.095823930927 | | 2009 | 22.845495297847 | | 2008 | 24.028390228748 | | 2007 | 25.898953894797 | | 2006 | 25.241380183251 | | 2005 | 27.118596049756 | | 2004 | 28.261089341713 | | 2003 | 26.834496624626 | | 2002 | 29.740059016437 |
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