Year Number 1961 6950 1962 7385 1963 7700 1964 8000 1965 8500 1966 9000 1967 9500 1968 10000 1969 10431 1970 10976 1971 11100 1972 11200 1973 11350 1974 11500 1975 11600 1976 11650 1977 11650 1978 11750 1979 11800 1980 11900 1981 11900 1982 11900 1983 11900 1984 12000 1985 12000 1986 12500 1987 12500 1988 12500 1989 12700 1990 12700 1991 12750 1992 12800 1993 13000 1994 13000 1995 13191