| Year | Value | | 2024 | 22,007 | | 2023 | 21,871 | | 2022 | 21,739 | | 2021 | 21,579 | | 2020 | 21,361 | | 2019 | 21,122 | | 2018 | 20,837 | | 2017 | 20,626 | | 2016 | 20,571 | | 2015 | 20,622 | | 2014 | 20,760 | | 2013 | 21,033 | | 2012 | 21,381 | | 2011 | 21,684 | | 2010 | 21,955 | | 2009 | 22,133 | | 2008 | 22,228 | | 2007 | 22,203 | | 2006 | 22,108 | | 2005 | 22,029 | | 2004 | 22,051 | | 2003 | 22,081 | | 2002 | 21,901 | | 2001 | 21,601 | | 2000 | 21,289 | | 1999 | 21,046 | | 1998 | 20,644 | | 1997 | 20,120 | | 1996 | 19,345 | | 1995 | 18,191 | | 1994 | 16,929 | | 1993 | 15,894 | | 1992 | 15,316 | | 1991 | 15,348 | | 1990 | 15,946 | | 1989 | 16,945 | | 1988 | 18,046 | | 1987 | 18,930 | | 1986 | 19,438 | | 1985 | 19,508 | | 1984 | 19,172 | | 1983 | 18,663 | | 1982 | 18,145 | | 1981 | 17,631 | | 1980 | 17,244 | | 1979 | 17,038 | | 1978 | 16,881 | | 1977 | 16,714 | | 1976 | 16,490 | | 1975 | 16,106 |
|