| Year | Value | | 2024 | 20,990 | | 2023 | 20,746 | | 2022 | 20,612 | | 2021 | 20,630 | | 2020 | 20,727 | | 2019 | 20,887 | | 2018 | 21,142 | | 2017 | 21,416 | | 2016 | 21,613 | | 2015 | 21,771 | | 2014 | 21,864 | | 2013 | 21,921 | | 2012 | 21,912 | | 2011 | 21,832 | | 2010 | 21,763 | | 2009 | 21,784 | | 2008 | 21,755 | | 2007 | 21,602 | | 2006 | 21,374 | | 2005 | 21,173 | | 2004 | 20,942 | | 2003 | 20,440 | | 2002 | 19,775 | | 2001 | 18,917 | | 2000 | 17,575 | | 1999 | 16,225 | | 1998 | 15,239 | | 1997 | 14,727 | | 1996 | 14,774 | | 1995 | 15,395 | | 1994 | 16,325 | | 1993 | 17,224 | | 1992 | 17,910 | | 1991 | 18,293 | | 1990 | 18,427 | | 1989 | 18,342 | | 1988 | 18,101 | | 1987 | 17,821 | | 1986 | 17,521 | | 1985 | 17,221 | | 1984 | 16,961 | | 1983 | 16,713 | | 1982 | 16,442 | | 1981 | 16,163 | | 1980 | 15,832 | | 1979 | 15,312 | | 1978 | 14,560 | | 1977 | 13,731 | | 1976 | 12,964 | | 1975 | 12,265 |
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