| Year | Value | | 2018 | 26.579414545736 | | 2017 | 26.669673283483 | | 2016 | 22.455016941978 | | 2015 | 12.173222255515 | | 2014 | 11.526851590822 | | 2013 | 9.1168711344675 | | 2012 | 12.740845652932 | | 2011 | 17.40562585311 | | 2010 | 19.933366140683 | | 2009 | 25.156963096575 | | 2008 | 14.635852116033 | | 2007 | 20.867093382643 | | 2006 | 10.929746941901 | | 2005 | 14.699997455641 | | 2004 | 15.406236869891 | | 2003 | 10.055458769482 | | 2002 | 16.893054193225 | | 2001 | 17.170072779632 | | 2000 | 14.665971305105 | | 1999 | 2.751078054289 | | 1998 | -7.9492900661032 | | 1997 | 13.945906154984 | | 1996 | 1.8155856606822 | | 1995 | 7.8134999473525 | | 1994 | 4.4467044395634 | | 1993 | 7.0564341606439 |
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