| Year | Value | | 2021 | 4,104 | | 2020 | 2,205 | | 2019 | 5,566 | | 2018 | 4,910 | | 2017 | 5,331 | | 2016 | 4,307 | | 2015 | 4,277 | | 2014 | 4,044 | | 2013 | 3,984 | | 2012 | 3,077 | | 2011 | 4,235 | | 2010 | 6,373 | | 2009 | 1,114 | | 2008 | 1,159 | | 2007 | 1,833 | | 2006 | 1,725 | | 2005 | 1,720 | | 2004 | 1,686 | | 2003 | 1,612 | | 2002 | 1,510 | | 2001 | 2,230 | | 2000 | 3,761 | | 1999 | 3,600 | | 1998 | 4,900 | | 1997 | 4,900 | | 1996 | 4,800 | | 1995 | 4,600 | | 1994 | 4,400 | | 1993 | 4,400 | | 1992 | 4,200 | | 1991 | 4,300 | | 1990 | 3,600 | | 1989 | 4,200 | | 1988 | 4,200 | | 1987 | 4,100 | | 1986 | 4,400 | | 1985 | 4,100 | | 1984 | 4,000 | | 1983 | 4,900 | | 1982 | 4,900 | | 1981 | 4,800 | | 1980 | 4,900 | | 1979 | 4,800 | | 1978 | 4,700 | | 1977 | 4,700 | | 1976 | 4,400 | | 1975 | 4,200 | | 1974 | 3,900 | | 1973 | 4,000 | | 1972 | 4,600 | | 1971 | 4,800 | | 1970 | 5,600 |
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