| Year | Value | | 1999 | 58,500 | | 1998 | 36,100 | | 1997 | 36,300 | | 1996 | 36,300 | | 1995 | 35,000 | | 1994 | 45,000 | | 1993 | 24,200 | | 1992 | 23,300 | | 1991 | 42,200 | | 1990 | 41,300 | | 1989 | 39,700 | | 1988 | 26,600 | | 1987 | 30,400 | | 1986 | 25,700 | | 1985 | 136,000 | | 1984 | 132,000 | | 1983 | 129,200 | | 1982 | 131,000 | | 1981 | 128,000 | | 1980 | 80,000 | | 1979 | 72,000 | | 1978 | 71,000 | | 1977 | 66,000 | | 1976 | 65,000 | | 1975 | 65,000 | | 1974 | 56,900 | | 1973 | 54,500 | | 1972 | 51,000 | | 1971 | 49,000 | | 1970 | 48,900 |
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