Year | Value | 2016 | 2.25 | 2015 | 2.29 | 2014 | 2.24 | 2013 | 2.3 | 2012 | 2.33 | 2011 | 2.27 | 2010 | 2.3 | 2009 | 2.3 | 2008 | 2.3 | 2007 | 2.3 | 2006 | 2.3 | 2005 | 2.2 | 2004 | 2.4 | 2002 | 2.5 | 1996 | 2.2100000381 | 1993 | 2.7000000477 | 1990 | 2.5 | 1985 | 3.3533000946045 | 1975 | 3.3817000389099 | 1970 | 2.974100112915 | 1960 | 3.775310754776 |
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