| Year | Value | | 2021 | 2.0540790067467 | | 2020 | 2.0508967195466 | | 2019 | 2.0481295393294 | | 2018 | 2.0447403144863 | | 2017 | 2.0433527807437 | | 2016 | 2.0413748197062 | | 2015 | 2.0414872675682 | | 2014 | 2.0400132260105 | | 2013 | 2.0385161150868 | | 2012 | 2.0370057868875 | | 2011 | 2.0355308751246 | | 2010 | 2.0340563250325 | | 2009 | 2.016441888334 | | 2008 | 1.9983819934866 | | 2007 | 1.9807747090498 | | 2006 | 1.9631691419928 | | 2005 | 1.94557044451 | | 2004 | 1.9279629718708 | | 2003 | 1.9103520644357 | | 2002 | 1.8927125264447 | | 2001 | 1.8751036187507 | | 2000 | 1.8574947110567 | | 1999 | 1.8540956864492 | | 1998 | 1.8506966618417 | | 1997 | 1.8472976372342 | | 1996 | 1.8438986126267 | | 1995 | 1.8404995880191 | | 1994 | 1.837100554504 | | 1993 | 1.8337015298965 | | 1992 | 1.8303025052889 | | 1991 | 1.8269067353867 | | 1990 | 1.8235077047237 |
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