| Year | Value | | 2019 | 1.1 | | 2018 | 1.11 | | 2017 | 1.14 | | 2016 | 1.15 | | 2015 | 1.16 | | 2014 | 1.17 | | 2013 | 1.18 | | 2012 | 1.2 | | 2011 | 1.23 | | 2010 | 1.24 | | 2009 | 1.24 | | 2008 | 1.25 | | 2007 | 1.3 | | 2006 | 1.32 | | 2005 | 1.35 | | 2004 | 1.5 | | 2003 | 1.54 | | 2002 | 1.57 | | 2001 | 1.61 | | 2000 | 1.65 | | 1998 | 1.6799999475 | | 1997 | 1.7100000381 | | 1996 | 1.75 | | 1995 | 1.7799999714 | | 1994 | 1.793900013 | | 1990 | 2.5 | | 1980 | 3.3143999576569 | | 1970 | 3.9395999908447 | | 1960 | 4.7907772064209 |
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