| Year | Value | | 2017 | 35.203141190445 | | 2016 | 26.372202748052 | | 2015 | 32.551071899023 | | 2014 | 31.767002819446 | | 2013 | 34.819268952514 | | 2012 | 36.417402751088 | | 2011 | 40.117794607105 | | 2010 | 41.572981524397 | | 2009 | 41.994908741477 | | 2008 | 45.680950325913 | | 2007 | 51.269264189178 | | 2006 | 47.580454127609 |
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