| Year | Value | | 2018 | 17,463 | | 2017 | 16,926 | | 2016 | 16,415 | | 2015 | 15,886 | | 2014 | 15,443 | | 2013 | 14,993 | | 2012 | 14,541 | | 2011 | 14,119 | | 2010 | 13,750 | | 2009 | 13,063 | | 2008 | 12,481 | | 2007 | 11,931 | | 2006 | 11,310 | | 2005 | 10,545 | | 2004 | 9,825 | | 2003 | 8,913 | | 2002 | 7,925 | | 2001 | 7,057 | | 2000 | 6,441 | | 1999 | 6,062 | | 1998 | 6,013 | | 1997 | 6,170 | | 1996 | 6,286 | | 1995 | 6,181 | | 1994 | 5,707 | | 1993 | 5,019 | | 1992 | 4,240 | | 1991 | 3,555 | | 1990 | 3,065 | | 1989 | 2,725 | | 1988 | 2,515 | | 1987 | 2,439 | | 1986 | 2,487 | | 1985 | 2,643 | | 1984 | 2,906 | | 1983 | 3,287 | | 1982 | 3,722 | | 1981 | 4,119 | | 1980 | 4,425 | | 1979 | 4,693 | | 1978 | 4,826 | | 1977 | 4,871 | | 1976 | 4,907 | | 1975 | 4,980 | | 1974 | 5,090 | | 1973 | 5,237 | | 1972 | 5,367 | | 1971 | 5,380 | | 1970 | 5,213 | | 1969 | 4,948 | | 1968 | 4,508 | | 1967 | 3,991 | | 1966 | 3,560 | | 1965 | 3,313 | | 1964 | 3,201 | | 1963 | 3,273 | | 1962 | 3,480 | | 1961 | 3,714 | | 1960 | 3,907 |
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