| Year | Value | | 2022 | 14.429450757576 | | 2021 | 5.0550270471927 | | 2020 | 3.3744697261859 | | 2019 | 2.227478809383 | | 2018 | 1.8129515654268 | | 2017 | 2.0759355367385 | | 2016 | 0.66476733143396 | | 2015 | 0.87412587412577 | | 2014 | 0.05382131323998 | | 2013 | 0.99198260633243 | | 2012 | 3.5603715170278 | | 2011 | 4.2394014962594 | | 2010 | 2.5806937025054 | | 2009 | 3.7953924248341 | | 2008 | 4.1649719352476 | | 2007 | 2.458743123854 | | 2006 | 1.2846939436641 | | 2005 | 2.1837987239026 | | 2004 | 3.3826468188469 | | 2003 | 0.68270137578768 | | 2002 | 1.9052821504805 | | 2001 | 5.4083354556615 | | 2000 | 9.9001753884306 | | 1999 | 7.1540729117986 | | 1998 | 11.597855425724 | | 1997 | 14.91315861496 | | 1996 | 19.794966919671 | | 1995 | 27.951388563304 | | 1994 | 32.991276609352 | | 1993 | 36.964166612072 | | 1992 | 46.098562103743 | | 1991 | 76.769499208735 | | 1990 | 567.87880066619 | | 1989 | 244.55093298483 | | 1988 | 58.720829732065 | | 1987 | 26.379027853632 | | 1986 | 16.549968173138 | | 1985 | 11.52126073685 | | 1984 | 15.400999426558 | | 1983 | 25.534759358289 | | 1982 | 103.55871886121 | | 1981 | 19.127182044888 | | 1980 | 9.6827133479213 | | 1979 | 7.0257611241219 | | 1978 | 8.1012658227847 | | 1977 | 4.9027895182156 | | 1976 | 4.4130626655289 | | 1975 | 2.2563176895509 | | 1974 | 7.0531400956523 | | 1973 | 2.4752475247523 | | 1972 | 0.098911967360076 | | 1971 | 1.0999999990001 |
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