| Year | Value | | 2022 | 17,968 | | 2021 | 18,297 | | 2020 | 18,640 | | 2019 | 18,925 | | 2018 | 18,940 | | 2017 | 18,763 | | 2016 | 18,567 | | 2015 | 18,323 | | 2014 | 18,133 | | 2013 | 18,068 | | 2012 | 18,093 | | 2011 | 18,229 | | 2010 | 18,486 | | 2009 | 18,675 | | 2008 | 18,692 | | 2007 | 18,636 | | 2006 | 18,527 | | 2005 | 18,369 | | 2004 | 18,165 | | 2003 | 17,900 | | 2002 | 17,565 | | 2001 | 17,142 | | 2000 | 16,723 | | 1999 | 16,342 | | 1998 | 15,982 | | 1997 | 15,694 | | 1996 | 15,500 | | 1995 | 15,358 | | 1994 | 15,239 | | 1993 | 15,137 | | 1992 | 14,993 | | 1991 | 14,816 | | 1990 | 14,640 | | 1989 | 14,480 | | 1988 | 14,328 | | 1987 | 14,180 | | 1986 | 14,015 | | 1985 | 13,830 | | 1984 | 13,646 | | 1983 | 13,470 | | 1982 | 13,282 | | 1981 | 13,055 | | 1980 | 12,739 | | 1979 | 12,373 | | 1978 | 12,021 | | 1977 | 11,670 | | 1976 | 11,325 | | 1975 | 10,991 | | 1974 | 10,714 | | 1973 | 10,584 | | 1972 | 10,602 | | 1971 | 10,705 | | 1970 | 10,876 | | 1969 | 10,991 | | 1968 | 10,925 | | 1967 | 10,722 | | 1966 | 10,433 | | 1965 | 10,079 | | 1964 | 9,691 | | 1963 | 9,310 | | 1962 | 8,979 | | 1961 | 8,699 | | 1960 | 8,455 |
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