| Year | Value | | 2021 | 2.16644 | | 2020 | 1.613892 | | 2019 | 10.8 | | 2018 | 11.13032 | | 2017 | 10.552031 | | 2016 | 6.027344 | | 2015 | 9.28416 | | 2014 | 11.818297385015 | | 2013 | 13.537781 | | 2012 | 15.744 | | 2011 | 16.867234240556 | | 2010 | 15.697712047082 | | 2009 | 9.099 | | 2008 | 10.63 | | 2007 | 10.241 | | 2006 | 10.04 | | 2005 | 10.351 | | 2004 | 10.173 | | 2003 | 9.735 | | 2002 | 12.506 | | 2001 | 22.948 | | 2000 | 79.005 | | 1999 | 84.8000030518 | | 1998 | 90.5 | | 1997 | 54.5 | | 1996 | 44.9000015259 | | 1995 | 43.7999992371 | | 1994 | 43.4000015259 | | 1993 | 37.9000015259 | | 1992 | 36.2000007629 | | 1991 | 36.0999984741 | | 1990 | 38.7000007629 | | 1989 | 32.7000007629 | | 1988 | 33.0999984741 | | 1987 | 30 | | 1986 | 24.7999992371 | | 1985 | 25.2999992371 | | 1984 | 24 | | 1983 | 21 | | 1982 | 21.5 | | 1981 | 20.8999996185 | | 1980 | 22.3999996185 | | 1979 | 22 | | 1978 | 18.8999996185 | | 1977 | 18.2999992371 | | 1976 | 13.1999998093 | | 1975 | 8.8999996185 | | 1974 | 9.1999998093 | | 1973 | 8.1000003815 | | 1972 | 8.6000003815 | | 1971 | 9.1999998093 | | 1970 | 9.3000001907 |
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