Year | Value | 2021 | 38,200 | 2020 | 38,200 | 2019 | 38,200 | 2018 | 38,200 | 2017 | 38,200 | 2016 | 38,200 | 2015 | 38,200 | 2014 | 38,200 | 2013 | 38,200 | 2012 | 38,500 | 2011 | 36,650 | 2010 | 36,650 | 2009 | 36,550 | 2008 | 36,350 | 2007 | 35,950 | 2006 | 35,700 | 2005 | 35,200 | 2004 | 34,800 | 2003 | 34,600 | 2002 | 34,400 | 2001 | 34,200 | 2000 | 34,000 | 1999 | 33,700 | 1998 | 33,500 | 1997 | 33,300 | 1996 | 32,900 | 1995 | 32,700 | 1994 | 32,500 | 1993 | 32,300 | 1992 | 32,050 | 1991 | 31,850 | 1990 | 31,600 | 1989 | 31,400 | 1988 | 31,400 | 1987 | 31,100 | 1986 | 30,900 | 1985 | 30,900 | 1984 | 30,850 | 1983 | 30,350 | 1982 | 30,350 | 1981 | 30,350 | 1980 | 30,350 | 1979 | 30,300 | 1978 | 29,800 | 1977 | 28,800 | 1976 | 28,800 | 1975 | 28,800 | 1974 | 28,800 | 1973 | 28,800 | 1972 | 28,800 | 1971 | 28,800 | 1970 | 30,750 | 1969 | 30,750 | 1968 | 30,750 | 1967 | 30,750 | 1966 | 30,750 | 1965 | 30,750 | 1964 | 30,700 | 1963 | 30,700 | 1962 | 30,700 | 1961 | 30,700 |
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