| Year | Value | | 2017 | 0.92178070141131 | | 2016 | 0.87249011726785 | | 2015 | 0.9198550855923 | | 2014 | 0.95035538546472 | | 2013 | 0.92980235098989 | | 2012 | 0.90943253649479 | | 2011 | 1.1396318921271 | | 2010 | 0.95584849987928 | | 2009 | 0.83911125045393 | | 2008 | 0.86678076981939 | | 2007 | 0.94925581904243 | | 2006 | 0.94288553068425 | | 2005 | 0.93459060604158 | | 2003 | 1.1887471658519 | | 2002 | 0.93894627040596 | | 2001 | 0.91636440464318 | | 2000 | 1.058403805567 | | 1991 | 1.0884367360857 | | 1985 | 1.1039620415433 | | 1980 | 1.034881606157 | | 1975 | 0.88689612562547 | | 1970 | 0.96168087241646 | | 1960 | 0.92264574204322 |
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