| Year | Value | | 2020 | 0.85224354935401 | | 2019 | 0.88327771829284 | | 2018 | 0.91221497959913 | | 2017 | 0.94235903879378 | | 2016 | 0.97406822257276 | | 2015 | 1.0065772510616 | | 2014 | 1.039857655041 | | 2013 | 1.0747390037666 | | 2012 | 1.1113933395812 | | 2011 | 1.1497684444969 | | 2010 | 1.1946460253616 | | 2009 | 1.2399652894503 | | 2008 | 1.2866018996402 | | 2007 | 1.3352067310853 | | 2006 | 1.3030197245203 | | 2005 | 1.4508964388239 | | 2004 | 1.5054695750978 | | 2003 | 1.7208179391828 | | 2002 | 1.5097262742742 | | 2001 | 2.0692765339917 | | 2000 | 1.7311203280377 | | 1999 | 1.9441212289957 | | 1998 | 2.0352251724222 | | 1997 | 2.049843370733 | | 1996 | 1.7996359120053 | | 1995 | 2.1358341500273 | | 1994 | 2.1704434794813 | | 1993 | 2.3870652394254 | | 1992 | 2.4598997898323 | | 1991 | 2.9727670753759 |
|