Year | Value | 2021 | 21,030 | 2020 | 20,760 | 2019 | 20,490 | 2018 | 20,220 | 2017 | 19,950 | 2016 | 19,680 | 2015 | 19,410 | 2014 | 19,140 | 2013 | 18,870 | 2012 | 18,600 | 2011 | 18,410 | 2010 | 18,330 | 2009 | 18,310 | 2008 | 18,280 | 2007 | 18,250 | 2006 | 18,220 | 2005 | 18,190 | 2004 | 18,480 | 2003 | 18,330 | 2002 | 18,340 | 2001 | 18,510 | 2000 | 18,670 | 1999 | 18,870 | 1998 | 19,130 | 1997 | 19,520 | 1996 | 19,930 | 1995 | 20,370 | 1994 | 20,730 | 1993 | 20,770 | 1992 | 20,820 | 1991 | 20,770 | 1990 | 20,820 | 1989 | 20,870 | 1988 | 20,920 | 1987 | 20,870 | 1986 | 20,820 | 1985 | 20,600 | 1984 | 20,600 | 1983 | 20,600 | 1982 | 20,600 | 1981 | 20,750 | 1980 | 20,880 | 1979 | 21,000 | 1978 | 21,200 | 1977 | 21,430 | 1976 | 20,950 | 1975 | 20,600 | 1974 | 20,300 | 1973 | 20,000 | 1972 | 19,060 | 1971 | 18,990 | 1970 | 18,800 | 1969 | 18,970 | 1968 | 16,760 | 1967 | 16,660 | 1966 | 16,210 | 1965 | 16,240 | 1964 | 16,050 | 1963 | 16,040 | 1962 | 15,900 | 1961 | 15,750 |
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