| Year | Value | | 2017 | 1.04 | | 2016 | 1.22 | | 2014 | 1.27 | | 2013 | 0.89 | | 2012 | 1.08 | | 2011 | 1.09 | | 2010 | 1.2 | | 2009 | 1.1 | | 2008 | 1.2 | | 2007 | 1.2 | | 2006 | 1.3 | | 2005 | 1.2 | | 2004 | 1.3 | | 2003 | 1.2999999523 | | 2000 | 1.9 | | 1996 | 2.1300001144 | | 1995 | 2.5 | | 1993 | 2.7999999523 | | 1990 | 2.7000000477 | | 1986 | 3.3168001174927 | | 1970 | 5.4014000892639 | | 1960 | 4.6677651405334 |
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