| Year | Value | | 2021 | 3.137035 | | 2020 | 1.782252 | | 2019 | 0.024356690607853 | | 2018 | 0.025638621692477 | | 2017 | 0.025670514 | | 2016 | 0.028381977 | | 2015 | 0.028042787566988 | | 2014 | 1.517388 | | 2013 | 1.517388 | | 2012 | 4.6633916578069 | | 2011 | 6.4607279530239 | | 2010 | 4.6709182 | | 2009 | 11.433 | | 2008 | 14.29 | | 2007 | 17.532 | | 2006 | 16.385 | | 2005 | 22.118 | | 2004 | 19.748 | | 2003 | 16.054 | | 2002 | 13.178 | | 2001 | 20.813 | | 2000 | 20.813 | | 1999 | 18 | | 1998 | 13.3000001907 | | 1997 | 15.6000003815 | | 1996 | 16.2000007629 | | 1995 | 16 | | 1994 | 12.6000003815 | | 1993 | 9.5 | | 1992 | 12.5 | | 1991 | 15.3999996185 | | 1990 | 17.7000007629 | | 1989 | 10 | | 1988 | 9.3999996185 | | 1987 | 13.5 | | 1986 | 12.5 | | 1985 | 15.6999998093 | | 1984 | 11.3000001907 | | 1983 | 9.3000001907 | | 1982 | 12.8999996185 | | 1981 | 17 | | 1980 | 16.2000007629 | | 1979 | 12.6999998093 | | 1978 | 13.1000003815 | | 1977 | 9.3999996185 | | 1976 | 8.8000001907 | | 1975 | 7.4000000954 | | 1974 | 5.0999999046 | | 1973 | 1.8999999762 | | 1972 | 2.2999999523 | | 1971 | 1.6000000238 | | 1970 | 1 |
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