| Year | Value | | 2020 | 1.5775559195477 | | 2019 | 1.6405794526627 | | 2018 | 1.653595960827 | | 2017 | 1.6816425135634 | | 2016 | 1.7039505037206 | | 2015 | 1.7462080968654 | | 2014 | 1.7803656625578 | | 2013 | 1.8178494851682 | | 2012 | 1.8416069689374 | | 2011 | 1.8757221358558 | | 2010 | 1.9139100196016 | | 2009 | 1.9420614387277 | | 2008 | 2.002675770212 | | 2007 | 2.0283162847578 | | 2006 | 1.9724212216167 | | 2005 | 1.9615831123961 | | 2004 | 1.9382479004707 | | 2003 | 1.9210575009046 | | 2002 | 2.0443062901263 | | 2001 | 2.0336070492152 | | 2000 | 2.0226490246466 | | 1999 | 1.9940924131478 | | 1998 | 2.0772409473172 | | 1997 | 2.5676566703726 | | 1996 | 2.6948219981217 | | 1995 | 3.1331156225998 | | 1994 | 1.2778945205416 | | 1993 | 1.2005663471648 | | 1992 | 1.1992514439824 |
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