Year | Value | 2020 | 2.293 | 2015 | 2.597 | 2014 | 2.602 | 2013 | 2.45 | 2012 | 2.433 | 2011 | 2.475 | 2010 | 2.47 | 2009 | 1.91 | 2008 | 1.884 | 2007 | 1.879 | 2006 | 1.461 | 2005 | 1.8 | 2004 | 1.5 | 2003 | 1.9 | 1997 | 1.89 | 1995 | 1.783 | 1986 | 1.566 | 1982 | 1.62 | 1981 | 1.412 | 1980 | 1.698 | 1970 | 0.954 | 1965 | 1.263 | 1960 | 0.871 |
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