| Year | Value | | 2022 | 7.8962761916855 | | 2021 | 5.6892084768375 | | 2020 | 3.3968341557001 | | 2019 | 3.6359614212705 | | 2018 | 4.8993501535655 | | 2017 | 6.0414572401899 | | 2016 | 2.8217078474766 | | 2015 | 2.7206406496402 | | 2014 | 4.0186160807868 | | 2013 | 3.806390697472 | | 2012 | 4.1115098107029 | | 2011 | 3.4073782460574 | | 2010 | 4.1567272268017 | | 2009 | 5.2973558422886 | | 2008 | 5.124982745759 | | 2007 | 3.9668490545824 | | 2006 | 3.6294676243913 | | 2005 | 3.9880571459744 | | 2004 | 4.6884088484314 | | 2003 | 4.5469001211872 | | 2002 | 5.030727331513 | | 2001 | 6.3677380623504 | | 2000 | 9.491561494354 | | 1999 | 16.585616970754 | | 1998 | 15.928395011935 | | 1997 | 20.625628725925 | | 1996 | 34.378383223517 | | 1995 | 34.999271288959 | | 1994 | 6.9658123719112 | | 1993 | 9.7514604535755 | | 1992 | 15.507896253357 | | 1991 | 22.662359455061 | | 1990 | 26.651672564677 | | 1989 | 20.007876713998 | | 1988 | 114.16225854907 | | 1987 | 131.82738392309 | | 1986 | 86.233316992354 | | 1985 | 57.74844840087 | | 1984 | 65.44880712776 | | 1983 | 101.87493843599 | | 1982 | 58.913419853105 | | 1981 | 27.93376259824 | | 1980 | 26.351651356283 | | 1979 | 18.191246298764 | | 1978 | 17.457292567826 | | 1977 | 29.064124710346 | | 1976 | 15.824722489347 | | 1975 | 14.944534640927 | | 1974 | 23.784015442579 | | 1973 | 12.081939461294 | | 1972 | 4.9436923637787 | | 1971 | 5.4690289937684 | | 1970 | 5.0034120548343 | | 1969 | 3.3670033671168 | | 1968 | 2.3339509346703 | | 1967 | 3.0169484750215 | | 1966 | 4.2157883773844 | | 1965 | 3.5680386574294 | | 1964 | 2.3379031723436 | | 1963 | 0.59405500846197 | | 1962 | 1.1989841781508 | | 1961 | 1.6087596908193 | | 1960 | 4.9275188690312 |
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