Year | Value | 2017 | 0.39 | 2016 | 0.5 | 2015 | 0.5 | 2014 | 0.5 | 2013 | 0.53 | 2012 | 0.53 | 2011 | 0.44 | 2010 | 0.43 | 2009 | 0.42 | 2008 | 0.42 | 2007 | 0.42 | 2006 | 0.42 | 2005 | 0.42 | 2004 | 0.39 | 2003 | 0.39 | 2002 | 0.39 | 2001 | 0.39 | 2000 | 0.3 | 1990 | 0.2497999966 | 1987 | 0.3091000020504 | 1981 | 0.27559998631477 | 1970 | 0.19900000095367 | 1960 | 0.17062699794769 |
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