| Year | Value | | 2024 | 20,620 | | 2023 | 20,921 | | 2022 | 21,299 | | 2021 | 21,632 | | 2020 | 21,867 | | 2019 | 21,965 | | 2018 | 21,971 | | 2017 | 21,854 | | 2016 | 21,631 | | 2015 | 21,445 | | 2014 | 21,394 | | 2013 | 21,299 | | 2012 | 21,114 | | 2011 | 20,865 | | 2010 | 20,652 | | 2009 | 20,415 | | 2008 | 19,910 | | 2007 | 19,306 | | 2006 | 18,582 | | 2005 | 17,309 | | 2004 | 15,821 | | 2003 | 14,749 | | 2002 | 14,121 | | 2001 | 14,036 | | 2000 | 14,633 | | 1999 | 15,674 | | 1998 | 16,632 | | 1997 | 17,359 | | 1996 | 17,776 | | 1995 | 17,862 | | 1994 | 17,647 | | 1993 | 17,272 | | 1992 | 16,854 | | 1991 | 16,501 | | 1990 | 16,245 | | 1989 | 16,107 | | 1988 | 16,062 | | 1987 | 16,030 | | 1986 | 15,936 | | 1985 | 15,691 | | 1984 | 15,194 | | 1983 | 14,431 | | 1982 | 13,541 | | 1981 | 12,704 | | 1980 | 11,990 | | 1979 | 11,305 | | 1978 | 10,528 | | 1977 | 9,678 | | 1976 | 8,886 | | 1975 | 8,305 |
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