| Year | Value | | 2009 | 8,731 | | 2008 | 9,388 | | 2007 | 9,186 | | 2006 | 8,666 | | 2005 | 8,934 | | 2004 | 8,343 | | 2003 | 7,032 | | 2002 | 8,404 | | 2001 | 9,550 | | 2000 | 10,852 | | 1999 | 10,300 | | 1998 | 9,900 | | 1997 | 8,200 | | 1996 | 6,700 | | 1995 | 9,000 | | 1994 | 9,000 | | 1993 | 8,500 | | 1992 | 5,100 | | 1991 | 5,000 | | 1990 | 5,000 | | 1989 | 7,700 | | 1988 | 5,200 | | 1987 | 5,800 | | 1986 | 5,600 | | 1985 | 8,100 | | 1984 | 8,500 | | 1983 | 8,500 | | 1982 | 10,500 | | 1981 | 11,000 | | 1980 | 13,000 | | 1979 | 11,900 | | 1978 | 10,900 | | 1977 | 11,900 | | 1976 | 12,200 | | 1975 | 10,400 | | 1974 | 10,400 | | 1973 | 5,000 | | 1972 | 4,800 | | 1971 | 7,000 | | 1970 | 6,800 |
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