| Year | Value | | 2021 | 6,340 | | 2020 | 6,340 | | 2019 | 6,340 | | 2018 | 6,340 | | 2017 | 6,340 | | 2016 | 6,440 | | 2015 | 6,440 | | 2014 | 6,440 | | 2013 | 6,440 | | 2012 | 6,440 | | 2011 | 6,440 | | 2010 | 6,440 | | 2009 | 6,220 | | 2008 | 5,660 | | 2007 | 4,960 | | 2006 | 4,960 | | 2005 | 4,850 | | 2004 | 4,780 | | 2003 | 4,710 | | 2002 | 4,910 | | 2001 | 4,840 | | 2000 | 5,060 | | 1999 | 5,670 | | 1998 | 5,670 | | 1997 | 5,570 | | 1996 | 5,570 | | 1995 | 5,570 | | 1994 | 5,570 | | 1993 | 5,470 | | 1992 | 5,480 | | 1991 | 5,820 | | 1990 | 5,820 | | 1989 | 5,780 | | 1988 | 5,980 | | 1987 | 5,850 | | 1986 | 5,800 | | 1985 | 5,730 | | 1984 | 5,730 | | 1983 | 5,870 | | 1982 | 6,060 | | 1981 | 5,850 | | 1980 | 5,630 | | 1979 | 5,700 | | 1978 | 5,810 | | 1977 | 5,740 | | 1976 | 5,670 | | 1975 | 5,680 | | 1974 | 5,740 | | 1973 | 5,470 | | 1972 | 5,420 | | 1971 | 5,370 | | 1970 | 5,340 | | 1969 | 5,330 | | 1968 | 5,310 | | 1967 | 5,310 | | 1966 | 5,290 | | 1965 | 5,280 | | 1964 | 5,270 | | 1963 | 5,260 | | 1962 | 5,250 | | 1961 | 5,240 |
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