Year | Value | 2017 | 18.24147857959 | 2016 | 19.176491143081 | 2015 | 18.719092695783 | 2014 | 18.113252792669 | 2013 | 18.164701757908 | 2012 | 17.154388272973 | 2011 | 18.048800099183 | 2010 | 18.214370833791 | 2009 | 19.133869570587 | 2008 | 18.68490272997 | 2007 | 18.269118946905 | 2006 | 17.632685229545 | 2005 | 17.639530528376 | 2004 | 17.2120653125 | 2003 | 16.16695423856 | 2002 | 16.664444444444 | 2001 | 16.489850746888 | 2000 | 17.051331453535 |
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