| Year | Value | | 2021 | 22,630 | | 2020 | 22,420 | | 2019 | 22,160 | | 2018 | 22,110 | | 2017 | 22,280 | | 2016 | 22,090 | | 2015 | 21,760 | | 2014 | 21,570 | | 2013 | 21,610 | | 2012 | 21,560 | | 2011 | 21,510 | | 2010 | 21,440 | | 2009 | 21,280 | | 2008 | 21,300 | | 2007 | 21,490 | | 2006 | 21,590 | | 2005 | 21,570 | | 2004 | 21,694 | | 2003 | 21,690 | | 2002 | 21,230 | | 2001 | 21,260 | | 2000 | 21,300 | | 1999 | 21,050 | | 1998 | 21,600 | | 1997 | 21,650 | | 1996 | 21,700 | | 1995 | 21,750 | | 1994 | 21,800 | | 1993 | 21,900 | | 1992 | 22,000 | | 1991 | 22,000 | | 1990 | 22,000 | | 1989 | 22,000 | | 1988 | 22,000 | | 1987 | 22,000 | | 1986 | 22,000 | | 1985 | 22,000 | | 1984 | 22,000 | | 1983 | 22,000 | | 1982 | 22,000 | | 1981 | 22,000 | | 1980 | 22,000 | | 1979 | 22,000 | | 1978 | 22,000 | | 1977 | 22,000 | | 1976 | 22,000 | | 1975 | 22,000 | | 1974 | 22,000 | | 1973 | 22,000 | | 1972 | 22,000 | | 1971 | 22,000 | | 1970 | 22,000 | | 1969 | 22,000 | | 1968 | 22,000 | | 1967 | 22,000 | | 1966 | 22,000 | | 1965 | 22,000 | | 1964 | 22,000 | | 1963 | 22,000 | | 1962 | 22,000 | | 1961 | 22,000 |
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