| Year | Value | | 2018 | 0.98 | | 2017 | 0.99 | | 2016 | 1 | | 2015 | 1 | | 2014 | 1.03 | | 2013 | 1.03 | | 2012 | 1.03 | | 2011 | 1.04 | | 2010 | 1.05 | | 2009 | 1.02 | | 2008 | 1.03 | | 2007 | 1.06 | | 2006 | 1.02 | | 2005 | 1.05 | | 2004 | 1.07 | | 2003 | 1.06 | | 2002 | 1.09 | | 2001 | 1.08 | | 2000 | 1.05 | | 1999 | 1.1000000238 | | 1998 | 1.1000000238 | | 1997 | 1.1000000238 | | 1996 | 1.2000000477 | | 1995 | 1.2000000477 | | 1994 | 1.2000000477 | | 1993 | 1.2000000477 | | 1992 | 1.2000000477 | | 1991 | 1.1000000238 | | 1990 | 1 | | 1980 | 0.69999998807907 |
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