| Year | Value | | 2014 | 19,969.736121556 | | 2013 | 19,483.653846916 | | 2012 | 18,942.167732434 | | 2011 | 18,889.063978609 | | 2010 | 18,442.790107486 | | 2009 | 17,542.87792731 | | 2008 | 18,562.73241692 | | 2007 | 20,501.051385253 | | 2006 | 21,230.075562756 | | 2005 | 21,024.01429837 | | 2004 | 18,900.931188516 | | 2003 | 19,786.548385107 | | 2002 | 19,663.942356519 | | 2001 | 19,228.846830636 | | 2000 | 18,697.237441703 | | 1999 | 18,980.456068415 | | 1998 | 19,393.7699633 | | 1997 | 19,238.695580892 | | 1996 | 18,836.644773025 | | 1995 | 18,902.524578503 | | 1994 | 18,969.952162143 | | 1993 | 20,228.146159946 | | 1992 | 17,450.899056757 | | 1991 | 13,533.427341408 | | 1990 | 14,972.420750728 | | 1989 | 14,809.662855327 | | 1988 | 14,786.784376118 | | 1987 | 14,148.082260778 | | 1986 | 15,839.767567904 | | 1985 | 15,378.417266187 | | 1984 | 14,868.194753552 | | 1983 | 5,474.6869842776 | | 1982 | 5,137.8840306176 | | 1981 | 4,806.1892271415 | | 1980 | 4,578.110564128 | | 1979 | 4,251.5510662048 | | 1978 | 3,662.6051639106 | | 1977 | 3,520.0436358562 | | 1976 | 2,999.5600645239 | | 1975 | 2,455.1410653909 | | 1974 | 2,124.6956142587 | | 1973 | 1,948.315097104 | | 1972 | 1,850.7627198809 | | 1971 | 1,861.5363302625 |
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