| Year | Value | | 2024 | 20,695 | | 2023 | 21,308 | | 2022 | 21,734 | | 2021 | 21,962 | | 2020 | 22,058 | | 2019 | 22,022 | | 2018 | 21,880 | | 2017 | 21,665 | | 2016 | 21,426 | | 2015 | 21,161 | | 2014 | 20,887 | | 2013 | 20,570 | | 2012 | 20,215 | | 2011 | 19,990 | | 2010 | 19,871 | | 2009 | 19,757 | | 2008 | 19,669 | | 2007 | 19,647 | | 2006 | 19,598 | | 2005 | 19,688 | | 2004 | 19,899 | | 2003 | 20,295 | | 2002 | 20,842 | | 2001 | 21,312 | | 2000 | 21,651 | | 1999 | 22,071 | | 1998 | 22,499 | | 1997 | 22,833 | | 1996 | 23,102 | | 1995 | 23,317 | | 1994 | 23,440 | | 1993 | 23,418 | | 1992 | 23,253 | | 1991 | 23,008 | | 1990 | 22,751 | | 1989 | 22,413 | | 1988 | 21,882 | | 1987 | 21,120 | | 1986 | 20,086 | | 1985 | 18,731 | | 1984 | 17,203 | | 1983 | 15,892 | | 1982 | 15,034 | | 1981 | 14,785 | | 1980 | 15,292 | | 1979 | 16,267 | | 1978 | 17,210 | | 1977 | 17,899 | | 1976 | 18,262 | | 1975 | 18,272 |
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