| Year | Value | | 2024 | 18,793 | | 2023 | 18,576 | | 2022 | 18,545 | | 2021 | 18,784 | | 2020 | 19,189 | | 2019 | 19,492 | | 2018 | 19,683 | | 2017 | 19,844 | | 2016 | 20,026 | | 2015 | 20,366 | | 2014 | 20,820 | | 2013 | 21,186 | | 2012 | 21,499 | | 2011 | 21,672 | | 2010 | 21,588 | | 2009 | 21,557 | | 2008 | 21,765 | | 2007 | 22,177 | | 2006 | 22,712 | | 2005 | 23,343 | | 2004 | 24,064 | | 2003 | 24,703 | | 2002 | 25,061 | | 2001 | 25,238 | | 2000 | 25,256 | | 1999 | 25,274 | | 1998 | 25,197 | | 1997 | 25,067 | | 1996 | 25,008 | | 1995 | 25,036 | | 1994 | 25,079 | | 1993 | 25,125 | | 1992 | 25,209 | | 1991 | 25,302 | | 1990 | 25,330 | | 1989 | 25,330 | | 1988 | 25,364 | | 1987 | 25,464 | | 1986 | 25,693 | | 1985 | 26,076 | | 1984 | 26,571 | | 1983 | 27,186 | | 1982 | 27,806 | | 1981 | 28,208 | | 1980 | 28,265 | | 1979 | 28,104 | | 1978 | 27,913 | | 1977 | 27,774 | | 1976 | 27,755 | | 1975 | 27,853 |
|