| Year | Value | | 2022 | 7.1722247601644 | | 2021 | 3.9411206077873 | | 2020 | 1.7145617000725 | | 2019 | 1.6196319018405 | | 2018 | 1.598297038017 | | 2017 | 1.8507876745254 | | 2016 | 0.64624028445452 | | 2015 | 0.2927046281361 | | 2014 | 1.227507505974 | | 2013 | 1.1344226644582 | | 2012 | 1.0599131844563 | | 2011 | 4.0279066739204 | | 2010 | 2.3020238595857 | | 2009 | 2.1156511055456 | | 2008 | 3.9589493731206 | | 2007 | 2.3761431029066 | | 2006 | 3.3654019617199 | | 2005 | 3.0370233261701 | | 2004 | 2.2902490284757 | | 2003 | 1.7535744475956 | | 2002 | 2.6770925771161 | | 2001 | 2.625816303929 | | 2000 | 2.6152344624632 | | 1999 | 0.11426712977752 | | 1998 | 1.2652440991541 | | 1997 | 1.1871483310563 | | 1996 | 2.2857130540219 | | 1995 | 3.7549441367755 | | 1994 | 1.7453779077374 | | 1993 | 1.2882077657439 | | 1992 | 1.0145602717124 | | 1991 | 2.6023928599977 | | 1990 | 6.098444148102 | | 1989 | 5.7159915513563 | | 1988 | 6.3752494441105 | | 1987 | 15.744300788893 | | 1986 | 13.213398064002 | | 1985 | 15.417655571992 | | 1984 | 6.1712534792444 | | 1983 | 7.3410758605734 | | 1982 | 16.163694123102 | | 1981 | 15.370159583185 | | 1980 | 17.150545424095 | | 1979 | 13.699595015664 | | 1978 | 11.95661797333 | | 1977 | 14.383549419462 | | 1976 | 16.906857005945 | | 1975 | 14.684983472399 | | 1974 | 11.109402012222 | | 1973 | 8.1666692732666 | | 1972 | 6.9328045920685 | | 1971 | 10.387568318814 | | 1970 | 6.5171810515548 | | 1969 | 4.9252424269513 | | 1968 | 4.3119249655019 | | 1967 | 6.0569200626752 | | 1966 | 2.7554807754282 | | 1965 | 3.3974897561108 | | 1964 | 3.4749054767661 | | 1963 | 1.9684985044189 | | 1962 | 2.6808539698746 | | 1961 | 1.7977042900921 | | 1960 | 0.69792923379648 |
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