| Year | Value | | 2020 | 0.87688938042875 | | 2019 | 0.86797582774533 | | 2018 | 0.87462377312336 | | 2017 | 0.87511133593504 | | 2016 | 0.89987903260543 | | 2015 | 0.90615598044951 | | 2014 | 0.91693461028497 | | 2013 | 0.93467763902786 | | 2012 | 0.94820570340519 | | 2011 | 0.97252161208905 | | 2010 | 1.0152604325493 | | 2009 | 0.99396928638588 | | 2008 | 1.0886455860298 | | 2007 | 1.1021218697996 | | 2006 | 1.1244092493972 | | 2005 | 1.1836405365522 | | 2004 | 1.1867980656968 | | 2003 | 1.2265799049496 | | 2002 | 1.3050646478584 | | 2001 | 1.3142889988204 | | 2000 | 1.3307654954896 | | 1999 | 1.466544674895 | | 1998 | 1.5425296696375 | | 1997 | 1.5966084396669 | | 1996 | 1.6990618955362 | | 1995 | 1.7498878522232 | | 1994 | 1.5504341733888 | | 1993 | 1.5603927139336 | | 1992 | 1.656777280796 | | 1991 | 1.7287793086316 |
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