| Year | Value | | 2021 | 11.647566428915 | | 2020 | 10.799119620354 | | 2019 | 10.938399737976 | | 2018 | 11.468767601532 | | 2017 | 10.288405674018 | | 2016 | 9.1831220996985 | | 2015 | 10.642094808822 | | 2014 | 13.255361304645 | | 2013 | 12.933492451261 | | 2012 | 13.754673041287 | | 2011 | 13.954203679675 | | 2010 | 13.048348846076 | | 2009 | 12.956352412329 | | 2008 | 15.818067823976 | | 2007 | 16.551313062416 | | 2006 | 16.568215758649 | | 2005 | 16.622909683256 | | 2004 | 13.234025389905 | | 2003 | 13.314030204371 | | 2002 | 13.634966068049 | | 2001 | 15.778699595813 | | 2000 | 13.725534454084 | | 1999 | 11.242872649645 |
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