| Year | Value | | 2020 | 1.611575848597 | | 2019 | 1.5199101851823 | | 2018 | 1.5380208236369 | | 2017 | 1.5736724113803 | | 2016 | 1.6246647463045 | | 2015 | 1.6758915988798 | | 2014 | 2.0757457509539 | | 2013 | 2.1022508320752 | | 2012 | 2.1787291751462 | | 2011 | 2.2222739592356 | | 2010 | 2.3165885964717 | | 2009 | 2.4113023027426 | | 2008 | 2.5117315893967 | | 2007 | 2.5893569306677 | | 2006 | 2.6045654286838 | | 2005 | 2.6580379087902 | | 2004 | 2.7046754354352 | | 2003 | 2.8452021302552 | | 2002 | 2.8243983836012 | | 2001 | 2.865934999336 | | 2000 | 3.6294815458601 | | 1999 | 3.5699436715343 | | 1998 | 3.5558928813683 | | 1997 | 3.655032577503 | | 1996 | 3.1523195268097 | | 1995 | 3.1286747758894 | | 1994 | 3.7338318405526 | | 1993 | 3.3941904422863 | | 1992 | 3.3269121723068 | | 1991 | 3.8256591910558 | | 1990 | 3.7779697495162 |
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