Year | Value | 2021 | 18,120 | 2020 | 18,144.5 | 2019 | 18,168 | 2018 | 18,230 | 2017 | 18,190 | 2016 | 18,150 | 2015 | 18,460 | 2014 | 18,391 | 2013 | 18,476 | 2012 | 18,417 | 2011 | 18,584 | 2010 | 18,723 | 2009 | 19,174 | 2008 | 19,293 | 2007 | 19,144 | 2006 | 19,196 | 2005 | 19,377 | 2004 | 19,494 | 2003 | 19,137 | 2002 | 19,401 | 2001 | 19,227 | 2000 | 19,596 | 1999 | 19,726 | 1998 | 19,158 | 1997 | 19,633 | 1996 | 19,506 | 1995 | 19,647 | 1994 | 19,504 | 1993 | 19,669 | 1992 | 19,638 | 1991 | 19,695 | 1990 | 20,180 | 1989 | 20,059 | 1988 | 20,154 | 1987 | 20,143 | 1986 | 20,180 | 1985 | 20,198 | 1984 | 20,149 | 1983 | 20,088 | 1982 | 20,274 | 1981 | 20,305 | 1980 | 20,372 | 1979 | 20,368 | 1978 | 20,503 | 1977 | 20,658 | 1976 | 20,799 | 1975 | 20,871 | 1974 | 20,991 | 1973 | 21,080 | 1972 | 21,217 | 1971 | 21,364 | 1970 | 22,013 | 1969 | 22,182 | 1968 | 22,347 | 1967 | 22,417 | 1966 | 22,481 | 1965 | 22,473 | 1964 | 22,578 | 1963 | 22,769 | 1962 | 22,873 | 1961 | 22,969 |
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