| Year | Value | | 2023 | 21,974 | | 2022 | 21,748 | | 2021 | 21,345 | | 2020 | 20,884 | | 2019 | 21,632 | | 2018 | 21,593 | | 2017 | 21,449 | | 2016 | 21,376 | | 2015 | 21,292 | | 2014 | 21,240 | | 2013 | 21,195 | | 2012 | 21,123 | | 2011 | 21,050 | | 2010 | 21,029 | | 2009 | 21,097 | | 2008 | 21,078 | | 2007 | 20,898 | | 2006 | 20,661 | | 2005 | 20,271 | | 2004 | 20,058 | | 2003 | 19,785 | | 2002 | 19,348 | | 2001 | 18,939 | | 2000 | 18,704 | | 1999 | 18,477 | | 1998 | 18,178 | | 1997 | 17,808 | | 1996 | 17,447 | | 1995 | 17,170 | | 1994 | 16,654 | | 1993 | 16,478 | | 1992 | 15,984 | | 1991 | 15,585 |
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