Year | Value | 2018 | 2.06 | 2017 | 2.11 | 2016 | 2.12 | 2015 | 2.14 | 2014 | 2.12 | 2013 | 2.17 | 2012 | 2.17 | 2011 | 2.22 | 2010 | 2.04 | 2009 | 2.27 | 2008 | 2.28 | 2007 | 2.29 | 2006 | 2.33 | 2005 | 2.31 | 2004 | 2.41 | 2003 | 2.51 | 2002 | 2.54 | 2001 | 2.62 | 2000 | 2.72 | 1996 | 2.6700000763 | 1993 | 3.0999999046 | 1990 | 3.1586000919 | 1989 | 3.1767001152039 | 1980 | 3.4063999652862 | 1970 | 3.7764000892639 | 1960 | 3.6742901802063 |
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