| Year | Value | | 2024 | 18,625 | | 2023 | 18,713 | | 2022 | 18,911 | | 2021 | 19,324 | | 2020 | 19,973 | | 2019 | 20,691 | | 2018 | 21,436 | | 2017 | 22,108 | | 2016 | 22,569 | | 2015 | 22,907 | | 2014 | 23,119 | | 2013 | 23,157 | | 2012 | 23,040 | | 2011 | 22,894 | | 2010 | 22,801 | | 2009 | 22,727 | | 2008 | 22,620 | | 2007 | 22,481 | | 2006 | 22,278 | | 2005 | 21,963 | | 2004 | 21,671 | | 2003 | 21,481 | | 2002 | 21,340 | | 2001 | 21,360 | | 2000 | 21,490 | | 1999 | 21,809 | | 1998 | 22,261 | | 1997 | 22,725 | | 1996 | 23,095 | | 1995 | 23,413 | | 1994 | 23,621 | | 1993 | 23,691 | | 1992 | 23,674 | | 1991 | 23,645 | | 1990 | 23,746 | | 1989 | 23,943 | | 1988 | 24,108 | | 1987 | 24,177 | | 1986 | 24,095 | | 1985 | 23,861 | | 1984 | 23,447 | | 1983 | 22,783 | | 1982 | 21,893 | | 1981 | 20,853 | | 1980 | 19,663 | | 1979 | 18,441 | | 1978 | 17,511 | | 1977 | 17,039 | | 1976 | 17,060 | | 1975 | 17,667 |
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