| Year | Value | | 2022 | 6.3360080777792 | | 2021 | 2.5269200906617 | | 2020 | 0.81995730212704 | | 2019 | 1.7433207565385 | | 2018 | 1.5281952430738 | | 2017 | 1.7307995911889 | | 2016 | 0.29083333333332 | | 2015 | 0.47474316143778 | | 2014 | 0.62854398544072 | | 2013 | 1.7340396351916 | | 2012 | 2.6628416550802 | | 2011 | 3.4106834106834 | | 2010 | 2.2736791162154 | | 2009 | 0.36804199788889 | | 2008 | 3.4018796302557 | | 2007 | 2.3124586178613 | | 2006 | 2.6663149457707 | | 2005 | 2.4876966516409 | | 2004 | 2.2256791642889 | | 2003 | 2.0498403056352 | | 2002 | 2.0740861357164 | | 2001 | 2.663821105791 | | 2000 | 3.1507670702259 | | 1999 | 1.0251967647493 | | 1998 | 0.95857011049467 | | 1997 | 1.3675126120794 | | 1996 | 1.1838596884357 | | 1995 | 1.8676942496911 | | 1994 | 2.1947646868907 | | 1993 | 3.5880981853516 | | 1992 | 3.1541737596179 | | 1991 | 3.1183565987485 | | 1990 | 3.2537665908364 | | 1989 | 3.3709588729044 | | 1988 | 1.436590566349 | | 1987 | 0.056662909389104 | | 1986 | 0.29456340854544 | | 1985 | 4.0935877853009 | | 1984 | 6.4358578078699 | | 1983 | 8.6692715980852 | | 1982 | 9.3570509942738 | | 1981 | 8.072943759346 | | 1980 | 6.2999000624459 | | 1979 | 4.5465277904217 | | 1978 | 3.0946607742465 | | 1977 | 6.7054941145067 | | 1976 | 9.797346437163 | | 1975 | 10.71767113392 | | 1974 | 9.5406554166059 | | 1973 | 6.068098359102 | | 1972 | 5.2256805055555 | | 1971 | 4.672214980414 | | 1970 | 4.6393534438995 | | 1969 | 2.2944343704717 | | 1968 | 2.6254290896315 | | 1967 | 2.1661569873985 | | 1966 | 3.3316797725456 | | 1965 | 3.3336793292935 | | 1964 | 3.0963815124574 | | 1963 | 2.8763224621267 | | 1962 | 0.8959466473399 | | 1961 | 0.48243359063082 | | 1960 | 0.44962029638986 |
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