Year | Value | 2017 | 1.4231318837789 | 2016 | 1.4775971516822 | 2015 | 1.5331177231741 | 2014 | 1.4958400027649 | 2010 | 1.6117793980703 | 2009 | 1.5167164223556 | 2008 | 1.6127100652336 | 2007 | 1.6749683638835 | 2006 | 1.7111680331166 | 2005 | 1.6726254323865 | 2004 | 1.6720612900593 | 2003 | 1.6436456899538 | 2002 | 1.6476293820395 | 2001 | 1.6167594325482 | 2000 | 1.640245192355 | 1990 | 1.7428748461062 | 1981 | 1.7487996940637 | 1980 | 1.7502481501881 | 1970 | 1.8984034962908 | 1960 | 1.8509316551825 |
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