| Year | Value | | 2021 | 3,007 | | 2020 | 1,790 | | 2019 | 4,105 | | 2018 | 3,988 | | 2017 | 3,863 | | 2016 | 3,861 | | 2015 | 3,875 | | 2014 | 3,672 | | 2013 | 3,780 | | 2012 | 3,856.2245630018 | | 2011 | 3,983.1502590674 | | 2010 | 4,235 | | 2009 | 1,433 | | 2008 | 1,413 | | 2007 | 1,614 | | 2006 | 1,512 | | 2005 | 1,471 | | 2004 | 1,415 | | 2003 | 1,285 | | 2002 | 1,257 | | 2001 | 1,983 | | 2000 | 3,368 | | 1999 | 3,300 | | 1998 | 1,800 | | 1997 | 1,800 | | 1996 | 3,300 | | 1995 | 3,100 | | 1994 | 3,000 | | 1993 | 3,000 | | 1992 | 2,800 | | 1991 | 2,900 | | 1990 | 2,200 | | 1989 | 2,800 | | 1988 | 2,800 | | 1987 | 2,700 | | 1986 | 3,600 | | 1985 | 2,400 | | 1984 | 2,300 | | 1983 | 2,300 | | 1982 | 2,300 | | 1981 | 2,200 | | 1980 | 2,300 | | 1979 | 1,600 | | 1978 | 1,600 | | 1977 | 1,500 | | 1976 | 1,600 | | 1975 | 1,400 | | 1974 | 1,300 | | 1973 | 1,300 | | 1972 | 1,200 | | 1971 | 1,500 | | 1970 | 1,600 |
|