| Year | Value | | 2020 | 1.4775130832743 | | 2019 | 1.3945124951266 | | 2018 | 1.4406939988251 | | 2017 | 1.494049893691 | | 2016 | 1.5162855038624 | | 2015 | 1.5515322718713 | | 2014 | 1.6427012621171 | | 2013 | 1.439984740883 | | 2012 | 1.4605768751892 | | 2011 | 0.98366028208887 | | 2010 | 1.0274498175301 | | 2009 | 1.0704392378039 | | 2008 | 1.0644916972309 | | 2007 | 1.7758320729479 | | 2006 | 1.8086669651431 | | 2005 | 1.1493077144982 | | 2004 | 1.138882318414 | | 2003 | 1.1815836870855 | | 2002 | 1.1857898546222 | | 2001 | 1.2165401413589 | | 2000 | 1.2167226359079 | | 1999 | 1.2465589450387 | | 1998 | 1.2791156680012 | | 1997 | 1.3138253004835 | | 1996 | 1.3521109018477 | | 1995 | 1.3896736342675 | | 1994 | 0.79584280657583 | | 1993 | 0.81636076020998 | | 1992 | 0.84015770523907 | | 1991 | 0.82794511906639 |
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