| Year | Value | | 2017 | 0.262714068 | | 2016 | 0.846429394 | | 2015 | 0.844630332 | | 2014 | 1.332792 | | 2013 | 1.31802 | | 2012 | 2.4180163947552 | | 2011 | 3.566035115998 | | 2010 | 5.2298048493098 | | 2004 | 6.652 | | 2003 | 16.63 | | 2002 | 18.901 | | 2001 | 32.97 | | 2000 | 39.949 | | 1999 | 31.3999996185 | | 1998 | 29.8999996185 | | 1997 | 32.7999992371 | | 1996 | 29.5 | | 1995 | 24.1000003815 | | 1994 | 23.7999992371 | | 1993 | 22.5 | | 1992 | 20.1000003815 | | 1991 | 19.1000003815 | | 1990 | 15.6999998093 | | 1989 | 13.6000003815 | | 1988 | 13.3999996185 | | 1987 | 12.1000003815 | | 1986 | 10.1000003815 | | 1985 | 9.3999996185 | | 1984 | 7.5 | | 1983 | 6.5999999046 | | 1982 | 4.5999999046 | | 1981 | 6.5 | | 1980 | 3.5999999046 | | 1979 | 2.7999999523 | | 1978 | 2.5 | | 1977 | 2.7000000477 | | 1976 | 2.7999999523 | | 1975 | 2.9000000954 | | 1974 | 3.0999999046 | | 1973 | 2.5 | | 1972 | 2.4000000954 | | 1971 | 3.0999999046 | | 1970 | 3.0999999046 |
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