| Year | Value | | 2020 | 1.6903116617771 | | 2019 | 1.6636512986878 | | 2018 | 1.6822891749949 | | 2017 | 1.676872883603 | | 2016 | 1.6429526808564 | | 2015 | 1.6419687204959 | | 2014 | 0.83951689999989 | | 2013 | 0.84468109593149 | | 2012 | 0.85831292157917 | | 2011 | 0.85904379834806 | | 2010 | 0.88752899723646 | | 2009 | 0.87133915024828 | | 2008 | 2.089241396449 | | 2007 | 2.1239230871557 | | 2006 | 2.1855107538632 | | 2005 | 2.1930963634999 | | 2004 | 1.9619950026833 | | 2003 | 2.3547445794703 | | 2002 | 2.3990991925042 | | 2001 | 3.1153730479492 | | 2000 | 2.8279351861323 | | 1999 | 2.8407717228374 | | 1998 | 3.3449982545191 | | 1997 | 2.8082825941664 | | 1996 | 2.1638480229199 | | 1995 | 2.1697679802854 | | 1994 | 1.2069627265771 | | 1993 | 1.1890040901741 | | 1992 | 1.1662038780944 |
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