| Year | Value | | 2020 | 1.3237717788036 | | 2019 | 1.29608201607 | | 2018 | 1.3654151903597 | | 2017 | 1.4035372257059 | | 2016 | 1.4018077713019 | | 2015 | 1.3954085477146 | | 2014 | 1.4094512160745 | | 2013 | 1.4450950583529 | | 2012 | 1.429096063505 | | 2011 | 1.4392474409427 | | 2010 | 1.490998960635 | | 2009 | 1.5333950257379 | | 2008 | 1.5382819562241 | | 2007 | 1.4309644611033 | | 2006 | 1.4557656508455 | | 2005 | 1.4850373208442 | | 2004 | 1.4234321606467 | | 2003 | 1.5350655609013 | | 2002 | 1.6171485207059 | | 2001 | 1.6543016918533 | | 2000 | 1.6946562187125 | | 1999 | 1.7358245432811 | | 1998 | 1.8483645235786 | | 1997 | 1.6520147373019 | | 1996 | 3.785041290846 | | 1995 | 3.5868998574467 | | 1994 | 2.11476848572 | | 1993 | 2.1613391657471 | | 1992 | 2.5878195032865 | | 1991 | 3.9400702603497 |
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