| Year | Value | | 2020 | 0.64123990147349 | | 2019 | 0.65527514511887 | | 2018 | 0.33909794182809 | | 2017 | 0.7026526719334 | | 2016 | 0.36474751720924 | | 2015 | 0.37922564020399 | | 2014 | 0.33996919199182 | | 2013 | 2.3868351932705 | | 2012 | 2.4290985930428 | | 2011 | 2.4701707624212 | | 2010 | 2.5112473469373 | | 2009 | 2.5872497928699 | | 2008 | 2.6685106461973 | | 2007 | 2.7506971422649 | | 2006 | 2.8347990065878 | | 2005 | 2.9173187473033 | | 2004 | 2.946938423505 | | 2003 | 3.0256784259389 | | 2002 | 3.0827219644505 | | 2001 | 2.8552941528642 | | 2000 | 3.1981439033358 | | 1999 | 3.2566417691665 | | 1998 | 3.4026911467369 | | 1997 | 3.8129859406894 | | 1996 | 3.0456433160094 | | 1995 | 1.9727661758311 | | 1994 | 2.049665473801 | | 1993 | 1.9756799966413 | | 1992 | 2.0530416132288 | | 1991 | 4.2234083237725 |
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