| Year | Value | | 2024 | 18,800 | | 2023 | 18,758 | | 2022 | 18,845 | | 2021 | 19,011 | | 2020 | 19,252 | | 2019 | 19,496 | | 2018 | 19,715 | | 2017 | 19,968 | | 2016 | 20,169 | | 2015 | 20,262 | | 2014 | 20,401 | | 2013 | 20,653 | | 2012 | 20,857 | | 2011 | 21,014 | | 2010 | 21,164 | | 2009 | 21,247 | | 2008 | 21,176 | | 2007 | 20,958 | | 2006 | 20,584 | | 2005 | 20,114 | | 2004 | 19,537 | | 2003 | 18,750 | | 2002 | 17,889 | | 2001 | 16,909 | | 2000 | 15,553 | | 1999 | 14,265 | | 1998 | 13,350 | | 1997 | 12,805 | | 1996 | 12,783 | | 1995 | 13,341 | | 1994 | 14,201 | | 1993 | 15,066 | | 1992 | 15,768 | | 1991 | 16,210 | | 1990 | 16,441 | | 1989 | 16,494 | | 1988 | 16,402 | | 1987 | 16,248 | | 1986 | 16,077 | | 1985 | 15,891 | | 1984 | 15,675 | | 1983 | 15,434 | | 1982 | 15,142 | | 1981 | 14,690 | | 1980 | 14,040 | | 1979 | 13,225 | | 1978 | 12,269 | | 1977 | 11,276 | | 1976 | 10,362 | | 1975 | 9,558 |
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