| Year | Value | | 2022 | 0.58628645999555 | | 2021 | 0.68352084532933 | | 2020 | 0.97530031867038 | | 2019 | 0.90245915630599 | | 2018 | 0.91067770694328 | | 2017 | 1.0736068605958 | | 2016 | 1.2621773178124 | | 2015 | 1.3542212887855 | | 2014 | 1.0897588237659 | | 2013 | 0.82694328769179 | | 2012 | 1.628186297268 | | 2011 | 1.4626147834683 | | 2010 | 1.8755128502518 | | 2009 | 3.4955307340169 | | 2008 | 3.6023074018726 | | 2007 | 3.5064383116047 | | 2006 | 3.4549651327021 | | 2005 | 3.3847254215101 | | 2004 | 3.2801562564658 | | 2003 | 3.2080402971321 | | 2002 | 3.0089288659272 | | 2001 | 2.7135444774825 | | 2000 | 2.6103774942688 | | 1999 | 2.6226771553429 | | 1998 | 2.5910661097094 | | 1997 | 2.5661292033247 | | 1996 | 2.4921667519021 | | 1995 | 2.3992676545846 | | 1994 | 2.3454607863943 | | 1993 | 2.274257211219 | | 1992 | 2.3706815569543 | | 1991 | 2.9837896498583 | | 1990 | 3.4261524869295 | | 1989 | 3.3556577950805 | | 1988 | 3.3162216783546 | | 1987 | 3.3200759409923 | | 1986 | 3.381065222556 | | 1985 | 3.4601795221816 | | 1984 | 3.4948506472262 | | 1983 | 3.5204428696094 | | 1982 | 3.5704319019143 | | 1981 | 3.2153693257679 | | 1980 | 2.1197063829361 | | 1979 | 1.3794599154932 | | 1978 | 1.3987554971504 | | 1977 | 1.4281876572533 | | 1976 | 1.4099702437942 | | 1975 | 1.3315254488815 | | 1974 | 1.2696064209073 | | 1973 | 1.1141896944532 | | 1972 | 0.95335407665366 | | 1971 | 2.392606655562 | | 1970 | 4.9641168065971 | | 1969 | 5.2697095278391 | | 1968 | 3.6740267895898 | | 1967 | 2.4036117083572 | | 1966 | 1.4978308124589 | | 1965 | 0.86428796293398 | | 1964 | 0.37811993627002 | | 1963 | 0.21490432390765 | | 1962 | 0.21536715741973 | | 1961 | 0.44486886206847 |
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