| Year | Value | | 2024 | 19,777 | | 2023 | 19,425 | | 2022 | 19,315 | | 2021 | 19,482 | | 2020 | 19,764 | | 2019 | 19,981 | | 2018 | 20,149 | | 2017 | 20,268 | | 2016 | 20,414 | | 2015 | 20,757 | | 2014 | 21,176 | | 2013 | 21,483 | | 2012 | 21,774 | | 2011 | 21,980 | | 2010 | 21,934 | | 2009 | 21,856 | | 2008 | 21,975 | | 2007 | 22,245 | | 2006 | 22,598 | | 2005 | 23,076 | | 2004 | 23,691 | | 2003 | 24,239 | | 2002 | 24,536 | | 2001 | 24,704 | | 2000 | 24,722 | | 1999 | 24,752 | | 1998 | 24,767 | | 1997 | 24,792 | | 1996 | 24,805 | | 1995 | 24,770 | | 1994 | 24,693 | | 1993 | 24,657 | | 1992 | 24,754 | | 1991 | 25,024 | | 1990 | 25,353 | | 1989 | 25,701 | | 1988 | 26,062 | | 1987 | 26,384 | | 1986 | 26,682 | | 1985 | 27,001 | | 1984 | 27,290 | | 1983 | 27,646 | | 1982 | 28,159 | | 1981 | 28,610 | | 1980 | 28,787 | | 1979 | 28,824 | | 1978 | 28,812 | | 1977 | 28,686 | | 1976 | 28,540 | | 1975 | 28,474 |
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