| Year | Value | | 2023 | 2.990670319922 | | 2022 | 2.5137734325422 | | 2021 | 1.6393166402584 | | 2020 | 1.6230862512591 | | 2019 | 2.1989322582617 | | 2018 | 2.678142769229 | | 2017 | 2.3455826764386 | | 2016 | 1.3880814958384 | | 2015 | 1.0419403866297 | | 2014 | 1.112504755228 | | 2013 | 0.94588590036915 | | 2012 | 0.53210073491698 | | 2011 | 0.3054683682244 | | 2010 | 0.14390300029404 | | 2009 | 0.34124197897088 | | 2008 | 1.8595721705992 | | 2007 | 2.5300854894066 | | 2006 | 2.3474224302839 | | 2005 | 1.5828919778046 | | 2004 | 0.8779361576874 | | 2003 | 0.69249762047619 | | 2002 | 0.89259637746296 | | 2001 | 1.3292952545682 | | 2000 | 1.3691928332981 | | 1999 | 1.2092387859574 | | 1998 | 1.0708590431972 | | 1997 | 0.81919709145882 | | 1996 | 0.5399130166093 | | 1995 | 0.54246799781155 | | 1994 | 0.86683594660681 | | 1993 | 1.0168119284382 | | 1992 | 1.2566320773965 | | 1991 | 1.1591494201002 | | 1990 | 0.7776621985854 | | 1989 | 1.2383960635672 | | 1988 | 1.5662175811481 | | 1987 | 1.0956291007245 | | 1986 | 0.7325888908986 | | 1985 | 0.78766761442324 | | 1984 | 1.0636254802733 | | 1983 | 1.3240444300149 | | 1982 | 1.3366104091596 | | 1981 | 1.1405832606108 | | 1980 | 1.0588964107677 | | 1979 | 0.97847964563084 | | 1978 | 0.7805382110656 | | 1977 | 0.74442648731923 | | 1976 | 0.99285735928341 | | 1975 | 1.278907889933 | | 1974 | 1.3529208106071 |
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