| Year | Value | | 2012 | 50,193 | | 2011 | 48,789 | | 2009 | 21,784 | | 2008 | 21,420 | | 2007 | 20,252 | | 2006 | 18,752 | | 2005 | 16,743 | | 2004 | 15,503 | | 2003 | 13,599 | | 2002 | 13,877 | | 2001 | 13,877 | | 2000 | 19,009 | | 1996 | 15,200 | | 1995 | 14,500 | | 1994 | 14,500 | | 1993 | 17,500 | | 1992 | 16,500 | | 1990 | 30,000 | | 1989 | 29,600 | | 1988 | 43,600 | | 1987 | 28,900 | | 1986 | 59,000 | | 1985 | 58,000 | | 1984 | 56,000 | | 1983 | 26,400 | | 1982 | 34,000 | | 1981 | 30,200 | | 1980 | 30,000 | | 1979 | 28,500 | | 1978 | 28,500 | | 1977 | 27,300 | | 1976 | 26,000 | | 1975 | 23,000 |
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