| Year | Value | | 2020 | 1.3713223918948 | | 2019 | 1.396458232807 | | 2018 | 1.4250491201407 | | 2017 | 1.465246127989 | | 2016 | 2.1271222436767 | | 2015 | 2.1751939022156 | | 2014 | 2.1900198677492 | | 2013 | 2.2109193205757 | | 2012 | 2.2293886133146 | | 2011 | 2.2489633027641 | | 2010 | 2.2723118413932 | | 2009 | 2.3001023106877 | | 2008 | 1.9333099565168 | | 2007 | 1.9574568421858 | | 2006 | 1.9834333352158 | | 2005 | 2.0131989008241 | | 2004 | 2.0423849443489 | | 2003 | 1.6316914398616 | | 2002 | 1.4669646808103 | | 2001 | 1.4121577918844 | | 2000 | 1.5058343552093 | | 1999 | 1.537801466755 | | 1998 | 1.5712937893391 | | 1997 | 1.5339967572022 | | 1996 | 1.2933370372563 | | 1995 | 1.1713030746706 | | 1994 | 0.66682822962059 | | 1993 | 0.68396659194495 | | 1992 | 0.70364403171143 | | 1991 | 0.7247164546871 |
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