| Year | Value | | 2020 | 1.447590167987 | | 2019 | 1.4705707814797 | | 2018 | 1.3980330475242 | | 2017 | 1.3914263028482 | | 2016 | 1.3611072551585 | | 2015 | 1.1872080007431 | | 2014 | 0.94136261500198 | | 2013 | 0.556446098303 | | 2012 | 0.97921971343159 | | 2011 | 0.97494798878236 | | 2010 | 0.97026883119834 | | 2009 | 0.965668110625 | | 2008 | 0.96180622735981 | | 2007 | 0.95745020056578 | | 2006 | 0.96130209128364 | | 2005 | 1.2117391692822 | | 2004 | 1.1947528219533 | | 2003 | 1.7656176327633 | | 2002 | 1.8073134586076 | | 2001 | 1.8200902761308 | | 2000 | 1.8124007442224 | | 1999 | 1.8346101519867 | | 1998 | 1.9168105909629 | | 1997 | 1.9228736808552 | | 1996 | 1.9647270879171 | | 1995 | 2.1650826905 | | 1994 | 1.4504458691322 | | 1993 | 1.5659373354736 | | 1992 | 1.7699921539952 |
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