| Year | Value | | 2022 | 7.8962761916855 | | 2021 | 4.2610512742281 | | 2020 | 1.3804264732029 | | 2019 | 2.0872308916201 | | 2018 | 2.2720598723016 | | 2017 | 2.6276229729427 | | 2016 | 2.7246122329529 | | 2015 | 3.1290027447393 | | 2014 | 3.4381665995861 | | 2013 | 2.76789666082 | | 2012 | 4.1115098107029 | | 2011 | 5.1289237668162 | | 2010 | 3.7333775770425 | | 2009 | 2.5919467343057 | | 2008 | 8.5581823351354 | | 2007 | 5.843975705316 | | 2006 | 4.2879098421574 | | 2005 | 4.695113049697 | | 2004 | 4.5602050738246 | | 2003 | 4.9246439266933 | | 2002 | 4.6354969691997 | | 2001 | 5.4219370367542 | | 2000 | 5.370701037352 | | 1999 | 3.5037978410894 | | 1998 | 5.4408722736669 | | 1997 | 7.0473388470902 | | 1996 | 9.7943018959802 | | 1995 | 11.669614643249 | | 1994 | 10.855321149439 | | 1993 | 10.835235920852 | | 1992 | 12.060323601829 | | 1991 | 22.662359455061 | | 1990 | 21.960175116508 | | 1989 | 14.329539032857 | | 1988 | 10.832703768991 | | 1987 | 13.550723782782 | | 1986 | 15.10537542098 | | 1985 | 18.686791297124 | | 1984 | 11.947427011886 | | 1983 | 11.582111084425 | | 1982 | 7.8127414121649 | | 1981 | 14.047968671887 | | 1980 | 18.098356915833 | | 1979 | 14.842308165533 | | 1978 | 10.507959934319 | | 1977 | 11.467932588065 | | 1976 | 10.069538030279 | | 1975 | 16.773570324582 | | 1974 | 23.244048532597 | | 1973 | 13.618317345838 | | 1972 | 5.9696235039256 | | 1971 | 4.3139356210801 | | 1970 | 3.9555092109977 | | 1969 | 2.4352027160153 | | 1968 | 3.9694541053439 | | 1967 | 2.1362586601549 | | 1966 | 3.4837761357541 | | 1965 | 2.6315789473685 | | 1964 | 3.3240331601813 | | 1963 | 2.9316184705135 | | 1962 | 2.1008403361344 | | 1961 | 2.4307939100916 | | 1960 | 2.0800000000782 |
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