| Year | Value | | 2020 | 2.5021708022365 | | 2019 | 2.5161509690581 | | 2018 | 2.6963623311024 | | 2017 | 2.3267766137051 | | 2016 | 2.0101545005427 | | 2015 | 1.9331879859839 | | 2014 | 1.8595093202815 | | 2013 | 1.5017244174917 | | 2012 | 1.5894701516565 | | 2011 | 1.5804631738543 | | 2010 | 1.7009140728401 | | 2009 | 1.6745940071562 | | 2008 | 1.5989606755609 | | 2007 | 1.5995659844296 | | 2006 | 1.5980876218126 | | 2005 | 1.8763449834946 | | 2004 | 1.766141428821 | | 2003 | 1.6283079852104 | | 2002 | 1.6818329391602 | | 2001 | 1.0459080671132 | | 2000 | 0.98417377425899 | | 1999 | 0.93245110157784 | | 1998 | 0.87546802299167 | | 1997 | 0.57656528870431 | | 1996 | 0.55931034210019 | | 1995 | 0.49523792565421 | | 1994 | 0.54809176371545 | | 1993 | 0.53989762461242 | | 1992 | 0.53218041767648 |
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