| Year | Value | | 2020 | 1.537428909085 | | 2019 | 1.46024866882 | | 2018 | 1.4546899491069 | | 2017 | 1.4526535297092 | | 2016 | 1.443836758095 | | 2015 | 1.4470016018595 | | 2014 | 1.4532690276225 | | 2013 | 1.4589589062485 | | 2012 | 1.4664539434403 | | 2011 | 1.4740920032559 | | 2010 | 1.4815352629921 | | 2009 | 1.4682768575064 | | 2008 | 1.516808331908 | | 2007 | 1.5257386080526 | | 2006 | 1.5370097798314 | | 2005 | 1.5515865789394 | | 2004 | 1.5462623128868 | | 2003 | 1.5071160824461 | | 2002 | 1.5188274903167 | | 2001 | 1.5300804315798 | | 2000 | 1.7986633696138 | | 1999 | 1.9673032057152 | | 1998 | 1.7168575855767 | | 1997 | 1.732518830177 | | 1996 | 2.6334191960769 | | 1995 | 2.7703374606148 | | 1994 | 3.1531240364672 | | 1993 | 3.9758305850878 | | 1992 | 3.9989397096998 | | 1991 | 6.8474879978752 | | 1990 | 6.9273835272418 |
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