| Year | Value | | 2021 | 4.8732943469786 | | 2020 | 4.8732943469786 | | 2019 | 4.8732943469786 | | 2018 | 4.8732943469786 | | 2017 | 4.8732943469786 | | 2016 | 4.8732943469786 | | 2015 | 4.8732943469786 | | 2014 | 4.8732943469786 | | 2013 | 4.8732943469786 | | 2012 | 4.8732943469786 | | 2011 | 4.8732943469786 | | 2010 | 4.8732943469786 | | 2009 | 4.8732943469786 | | 2008 | 4.8732943469786 | | 2007 | 4.8732943469786 | | 2006 | 4.8732943469786 | | 2005 | 4.8732943469786 | | 2004 | 5.0682261208577 | | 2003 | 5.8479532163743 | | 2002 | 5.8479532163743 | | 2001 | 5.8479532163743 | | 2000 | 6.82261208577 | | 1999 | 6.82261208577 | | 1998 | 6.82261208577 | | 1997 | 6.82261208577 | | 1996 | 7.7972709551657 | | 1995 | 7.7972709551657 | | 1994 | 7.7972709551657 | | 1993 | 7.7972709551657 | | 1992 | 7.7972709551657 | | 1991 | 7.7972709551657 | | 1990 | 7.0175438596491 | | 1989 | 7.0175438596491 | | 1988 | 7.0175438596491 | | 1987 | 6.82261208577 | | 1986 | 6.82261208577 | | 1985 | 6.82261208577 | | 1984 | 7.4074074074074 | | 1983 | 7.4074074074074 | | 1982 | 8.7719298245614 | | 1981 | 10.136452241715 | | 1980 | 11.695906432748 | | 1979 | 12.670565302144 | | 1978 | 12.670565302144 | | 1977 | 12.670565302144 | | 1976 | 12.670565302144 | | 1975 | 12.670565302144 | | 1974 | 13.64522417154 | | 1973 | 13.450292397661 | | 1972 | 11.695906432748 | | 1971 | 11.695906432748 | | 1970 | 11.111111111111 | | 1969 | 11.111111111111 | | 1968 | 11.111111111111 | | 1967 | 11.111111111111 | | 1966 | 11.111111111111 | | 1965 | 11.111111111111 | | 1964 | 11.111111111111 | | 1963 | 11.111111111111 | | 1962 | 11.111111111111 | | 1961 | 11.111111111111 |
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