| Year | Value | | 2021 | 15.983346024448 | | 2020 | 13.431586267867 | | 2019 | 15.640607865056 | | 2018 | 15.292412084557 | | 2017 | 15.260721225901 | | 2016 | 14.13915330495 | | 2015 | 13.28020070244 | | 2014 | 13.663827512341 | | 2013 | 14.948641958964 | | 2012 | 13.889962428562 | | 2011 | 12.219491358312 | | 2010 | 11.310064652648 | | 2009 | 11.12763172735 | | 2008 | 10.548876346235 | | 2007 | 11.279189116277 | | 2006 | 10.778408261422 | | 2005 | 10.449734075575 | | 2004 | 11.291019659814 | | 2003 | 9.861311204488 | | 2002 | 9.6613837680154 |
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