| Year | Value | | 2024 | 19,039 | | 2023 | 19,007 | | 2022 | 18,849 | | 2021 | 18,775 | | 2020 | 18,973 | | 2019 | 19,365 | | 2018 | 19,779 | | 2017 | 20,230 | | 2016 | 20,615 | | 2015 | 20,768 | | 2014 | 20,909 | | 2013 | 21,130 | | 2012 | 21,362 | | 2011 | 21,640 | | 2010 | 22,131 | | 2009 | 22,786 | | 2008 | 23,465 | | 2007 | 24,096 | | 2006 | 24,590 | | 2005 | 24,962 | | 2004 | 25,178 | | 2003 | 25,062 | | 2002 | 24,643 | | 2001 | 24,307 | | 2000 | 24,091 | | 1999 | 24,041 | | 1998 | 24,025 | | 1997 | 24,080 | | 1996 | 24,129 | | 1995 | 24,116 | | 1994 | 24,091 | | 1993 | 24,075 | | 1992 | 24,082 | | 1991 | 24,152 | | 1990 | 24,334 | | 1989 | 24,717 | | 1988 | 25,325 | | 1987 | 26,048 | | 1986 | 26,712 | | 1985 | 27,181 | | 1984 | 27,404 | | 1983 | 27,381 | | 1982 | 27,184 | | 1981 | 26,950 | | 1980 | 26,776 | | 1979 | 26,728 | | 1978 | 26,776 | | 1977 | 26,788 | | 1976 | 26,662 | | 1975 | 26,398 |
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