| Year | Value | | 2020 | 1.3452020483527 | | 2019 | 1.3200846243722 | | 2018 | 1.3052203770011 | | 2017 | 1.3293287973723 | | 2016 | 1.3760705856149 | | 2015 | 1.3909895683383 | | 2014 | 1.3890691912939 | | 2013 | 1.4216422993749 | | 2012 | 1.4307312556993 | | 2011 | 1.4960907480494 | | 2010 | 1.4640654624799 | | 2009 | 1.3283640809481 | | 2008 | 1.7568840742206 | | 2007 | 1.7814929442051 | | 2006 | 1.7952422571303 | | 2005 | 1.8201800374843 | | 2004 | 1.808464581465 | | 2003 | 1.8758164890752 | | 2002 | 1.9737242047423 | | 2001 | 2.0450730541539 | | 2000 | 2.1414559567932 | | 1999 | 2.2253882815801 | | 1998 | 2.3813004866001 | | 1997 | 2.5147893771903 | | 1996 | 2.5215685484655 | | 1995 | 2.5518314035963 | | 1994 | 1.8891341682151 | | 1993 | 1.9345957874908 | | 1992 | 2.0112329280592 | | 1991 | 1.9536671923394 |
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