| Year | Value | | 2023 | 0.64162085989163 | | 2022 | 0.50813788436894 | | 2021 | 0.35241699733603 | | 2020 | 0.47199444490691 | | 2019 | 0.65744108499639 | | 2018 | 0.720668948364 | | 2017 | 0.76579375896622 | | 2016 | 0.83152812218736 | | 2015 | 0.91222742827164 | | 2014 | 0.89858254726548 | | 2013 | 0.93499406579891 | | 2012 | 1.0818369983833 | | 2011 | 1.2454535327817 | | 2010 | 1.406955893151 | | 2009 | 1.4399881030751 | | 2008 | 1.4238346420155 | | 2007 | 1.4083827743079 | | 2006 | 1.3876659568261 | | 2005 | 1.3649213989886 | | 2004 | 1.3495338908262 | | 2003 | 1.334756883574 | | 2002 | 1.3188302563401 | | 2001 | 1.4090420094292 | | 2000 | 1.469762357668 | | 1999 | 1.5335301393607 | | 1998 | 1.6711575054798 | | 1997 | 1.7031677955137 | | 1996 | 1.779737854065 | | 1995 | 1.872513859917 | | 1994 | 2.003980069656 | | 1993 | 2.1718440834979 | | 1992 | 2.1200333106114 | | 1991 | 1.9677371609424 | | 1990 | 1.9345141971887 | | 1989 | 1.916989180722 | | 1988 | 1.8734440619762 | | 1987 | 1.9012384964141 | | 1986 | 1.9604484219087 | | 1985 | 1.9581780316218 | | 1984 | 1.9173714863649 | | 1983 | 1.8811766379094 | | 1982 | 1.8347383942061 | | 1981 | 1.8614332212288 | | 1980 | 1.9523249828863 | | 1979 | 2.0302601870252 | | 1978 | 2.1065283693908 | | 1977 | 2.1305080615746 | | 1976 | 2.0663664756253 | | 1975 | 2.0588844814463 | | 1974 | 2.1486529207952 |
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