| Year | Value | | 2024 | 22,414 | | 2023 | 22,444 | | 2022 | 22,389 | | 2021 | 22,337 | | 2020 | 22,250 | | 2019 | 22,101 | | 2018 | 21,943 | | 2017 | 21,756 | | 2016 | 21,552 | | 2015 | 21,329 | | 2014 | 21,103 | | 2013 | 20,836 | | 2012 | 20,651 | | 2011 | 20,640 | | 2010 | 20,744 | | 2009 | 20,927 | | 2008 | 21,238 | | 2007 | 21,605 | | 2006 | 21,878 | | 2005 | 22,179 | | 2004 | 22,413 | | 2003 | 22,503 | | 2002 | 22,433 | | 2001 | 22,307 | | 2000 | 22,181 | | 1999 | 22,210 | | 1998 | 22,252 | | 1997 | 22,188 | | 1996 | 22,042 | | 1995 | 21,856 | | 1994 | 21,582 | | 1993 | 21,153 | | 1992 | 20,529 | | 1991 | 19,641 | | 1990 | 18,585 | | 1989 | 17,510 | | 1988 | 16,612 | | 1987 | 16,169 | | 1986 | 16,289 | | 1985 | 16,948 | | 1984 | 17,932 | | 1983 | 18,831 | | 1982 | 19,396 | | 1981 | 19,639 | | 1980 | 19,572 | | 1979 | 19,241 | | 1978 | 18,865 | | 1977 | 18,530 | | 1976 | 18,138 | | 1975 | 17,752 |
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