| Year | Value | | 2020 | 1.5952058746115 | | 2019 | 1.5205904235387 | | 2018 | 1.5403716564192 | | 2017 | 1.5630122819272 | | 2016 | 1.5523779812203 | | 2015 | 1.5850626749059 | | 2014 | 1.5856277175367 | | 2013 | 1.2277853527108 | | 2012 | 1.2520030110091 | | 2011 | 1.2832059330993 | | 2010 | 1.3027487999679 | | 2009 | 1.3095365691109 | | 2008 | 1.3368344893576 | | 2007 | 1.3439727100232 | | 2006 | 1.1607622559912 | | 2005 | 0.67207857942751 | | 2004 | 0.63932078559738 | | 2003 | 1.154143164115 | | 2002 | 1.2500737890778 | | 2001 | 1.2517183963923 | | 2000 | 1.2547390360642 | | 1999 | 1.6008089771268 | | 1998 | 1.612247442099 | | 1997 | 1.8744725146188 | | 1996 | 1.9006380310143 | | 1995 | 1.8014224218604 | | 1994 | 1.410530077203 | | 1993 | 2.3881865670842 | | 1992 | 2.4739815400586 | | 1991 | 3.1014595985781 |
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