| Year | Value | | 2024 | 17,695 | | 2023 | 17,727 | | 2022 | 17,759 | | 2021 | 17,783 | | 2020 | 17,792 | | 2019 | 17,798 | | 2018 | 17,814 | | 2017 | 17,812 | | 2016 | 17,797 | | 2015 | 17,770 | | 2014 | 17,715 | | 2013 | 17,648 | | 2012 | 17,765 | | 2011 | 18,078 | | 2010 | 18,396 | | 2009 | 18,709 | | 2008 | 19,009 | | 2007 | 19,302 | | 2006 | 19,593 | | 2005 | 19,819 | | 2004 | 19,820 | | 2003 | 19,659 | | 2002 | 19,503 | | 2001 | 19,352 | | 2000 | 19,178 | | 1999 | 18,901 | | 1998 | 18,524 | | 1997 | 18,108 | | 1996 | 17,654 | | 1995 | 17,195 | | 1994 | 16,770 | | 1993 | 16,372 | | 1992 | 15,989 | | 1991 | 15,614 | | 1990 | 15,259 | | 1989 | 14,945 | | 1988 | 14,645 | | 1987 | 14,334 | | 1986 | 14,024 | | 1985 | 13,688 | | 1984 | 13,337 | | 1983 | 13,006 | | 1982 | 12,694 | | 1981 | 12,402 | | 1980 | 12,271 | | 1979 | 12,337 | | 1978 | 12,440 | | 1977 | 12,525 | | 1976 | 12,598 | | 1975 | 12,655 |
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