| Year | Value | | 2024 | 21,741 | | 2023 | 21,545 | | 2022 | 21,298 | | 2021 | 21,055 | | 2020 | 20,796 | | 2019 | 20,515 | | 2018 | 20,204 | | 2017 | 19,870 | | 2016 | 19,677 | | 2015 | 19,552 | | 2014 | 19,424 | | 2013 | 19,369 | | 2012 | 19,416 | | 2011 | 19,522 | | 2010 | 19,707 | | 2009 | 19,900 | | 2008 | 20,111 | | 2007 | 20,379 | | 2006 | 20,619 | | 2005 | 20,761 | | 2004 | 20,936 | | 2003 | 21,226 | | 2002 | 21,456 | | 2001 | 21,641 | | 2000 | 21,826 | | 1999 | 22,093 | | 1998 | 22,248 | | 1997 | 22,271 | | 1996 | 22,122 | | 1995 | 21,807 | | 1994 | 21,310 | | 1993 | 20,613 | | 1992 | 19,724 | | 1991 | 18,628 | | 1990 | 17,442 | | 1989 | 16,273 | | 1988 | 15,269 | | 1987 | 14,676 | | 1986 | 14,630 | | 1985 | 15,169 | | 1984 | 16,092 | | 1983 | 17,020 | | 1982 | 17,692 | | 1981 | 18,023 | | 1980 | 18,014 | | 1979 | 17,774 | | 1978 | 17,448 | | 1977 | 17,134 | | 1976 | 16,852 | | 1975 | 16,578 |
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