| Year | Value | | 2021 | 5.9135676925103 | | 2020 | 6.2280413761178 | | 2019 | 6.1697697147996 | | 2018 | 5.7143351256672 | | 2017 | 6.2176262310432 | | 2016 | 7.2728084433032 | | 2015 | 6.522200863461 | | 2014 | 7.5457937756543 | | 2013 | 8.8753760752574 | | 2012 | 9.7198795823815 | | 2011 | 9.4379997210443 | | 2010 | 9.2577575506827 | | 2009 | 9.4828957836118 | | 2008 | 9.8021197083869 | | 2006 | 7.6597080521111 | | 2005 | 7.5423981670364 | | 2004 | 9.0597499891693 | | 2003 | 8.9848112990753 | | 2002 | 8.7148337379422 | | 2001 | 7.3811226199899 | | 2000 | 6.42021503103 | | 1999 | 8.7375292750844 |
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