Year | Value | 2021 | 19,700 | 2020 | 19,690 | 2019 | 19,600 | 2018 | 19,380 | 2017 | 19,330 | 2016 | 19,310 | 2015 | 18,845 | 2014 | 18,720 | 2013 | 18,770 | 2012 | 18,410 | 2011 | 18,160 | 2010 | 18,050 | 2009 | 18,330 | 2008 | 18,250 | 2007 | 18,390 | 2006 | 18,550 | 2005 | 17,340 | 2004 | 16,420 | 2003 | 15,820 | 2002 | 15,950 | 2001 | 15,810 | 2000 | 15,880 | 1999 | 16,170 | 1998 | 17,490 | 1997 | 17,720 | 1996 | 18,740 | 1995 | 18,320 | 1994 | 25,400 | 1993 | 25,140 | 1992 | 25,300 | 1991 | 25,300 | 1990 | 25,300 | 1989 | 25,300 | 1988 | 25,300 | 1987 | 25,300 | 1986 | 25,300 | 1985 | 25,300 | 1984 | 25,300 | 1983 | 25,300 | 1982 | 25,300 | 1981 | 25,300 | 1980 | 25,300 | 1979 | 25,300 | 1978 | 25,300 | 1977 | 25,300 | 1976 | 25,300 | 1975 | 25,300 | 1974 | 25,300 | 1973 | 25,300 | 1972 | 25,300 | 1971 | 25,300 | 1970 | 25,300 | 1969 | 25,300 | 1968 | 25,300 | 1967 | 25,300 | 1966 | 25,300 | 1965 | 25,300 | 1964 | 25,300 | 1963 | 25,300 | 1962 | 25,300 | 1961 | 25,300 |
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