| Year | Value | | 2021 | 3,805 | | 2020 | 3,792 | | 2019 | 13,647 | | 2018 | 13,978 | | 2017 | 13,494 | | 2016 | 15,482 | | 2015 | 13,116 | | 2014 | 13,716 | | 2013 | 14,496 | | 2012 | 13,072 | | 2011 | 12,282 | | 2010 | 17,060 | | 2009 | 3,236 | | 2008 | 3,361 | | 2007 | 5,277 | | 2006 | 4,965 | | 2005 | 4,948 | | 2004 | 4,849 | | 2003 | 4,633 | | 2002 | 4,343 | | 2001 | 4,354 | | 2000 | 4,399 | | 1999 | 5,100 | | 1998 | 7,400 | | 1997 | 7,300 | | 1996 | 7,700 | | 1995 | 7,300 | | 1994 | 7,600 | | 1993 | 5,600 | | 1992 | 6,900 | | 1991 | 7,000 | | 1990 | 6,900 | | 1989 | 6,800 | | 1988 | 11,000 | | 1987 | 11,100 | | 1986 | 11,100 | | 1985 | 13,100 | | 1984 | 10,700 | | 1983 | 22,400 | | 1982 | 13,900 | | 1981 | 15,000 | | 1980 | 12,800 | | 1979 | 11,900 | | 1978 | 5,000 | | 1977 | 4,800 | | 1976 | 2,600 |
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