| Year | Value | | 2017 | 1 | | 2016 | 1.1 | | 2015 | 1.1 | | 2014 | 1.1 | | 2013 | 0.85 | | 2012 | 0.85 | | 2011 | 0.85 | | 2010 | 1.13 | | 2009 | 1.13 | | 2008 | 1.1 | | 2007 | 0.87 | | 2006 | 0.87 | | 2005 | 0.87 | | 2004 | 0.87 | | 2003 | 0.78 | | 2002 | 1.09 | | 2001 | 0.87 | | 2000 | 1.1 | | 1997 | 0.9800000191 | | 1994 | 1.1123000383 | | 1990 | 1.2899999619 | | 1985 | 1.2668999433518 | | 1981 | 1.2281999588013 | | 1975 | 1.4285999536514 | | 1970 | 1.4742000102997 | | 1960 | 1.5984001159668 |
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