| Year | Value | | 2024 | 19,557 | | 2023 | 19,525 | | 2022 | 19,368 | | 2021 | 19,298 | | 2020 | 19,515 | | 2019 | 19,871 | | 2018 | 20,213 | | 2017 | 20,619 | | 2016 | 21,003 | | 2015 | 21,185 | | 2014 | 21,300 | | 2013 | 21,490 | | 2012 | 21,716 | | 2011 | 21,975 | | 2010 | 22,388 | | 2009 | 22,972 | | 2008 | 23,533 | | 2007 | 23,934 | | 2006 | 24,220 | | 2005 | 24,405 | | 2004 | 24,449 | | 2003 | 24,330 | | 2002 | 24,049 | | 2001 | 23,741 | | 2000 | 23,407 | | 1999 | 23,217 | | 1998 | 23,099 | | 1997 | 23,103 | | 1996 | 23,304 | | 1995 | 23,639 | | 1994 | 24,047 | | 1993 | 24,518 | | 1992 | 25,020 | | 1991 | 25,478 | | 1990 | 25,791 | | 1989 | 26,061 | | 1988 | 26,473 | | 1987 | 27,021 | | 1986 | 27,577 | | 1985 | 28,016 | | 1984 | 28,354 | | 1983 | 28,559 | | 1982 | 28,563 | | 1981 | 28,420 | | 1980 | 28,204 | | 1979 | 28,027 | | 1978 | 27,885 | | 1977 | 27,689 | | 1976 | 27,405 | | 1975 | 27,026 |
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