| Year | Value | | 2015 | 11.801609076583 | | 2014 | 11.446942954335 | | 2013 | 11.974857545682 | | 2012 | 12.024330926114 | | 2011 | 11.84955131037 | | 2009 | 11.206579640974 | | 2008 | 12.152045529083 | | 2007 | 12.532512799322 | | 2006 | 12.125375587061 | | 2005 | 11.140296163859 | | 2004 | 10.524924556636 | | 2003 | 10.14362064445 | | 2002 | 9.8799686615269 | | 1999 | 10.387935326467 | | 1997 | 11.200453886382 |
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