1963 12.9
1964 12.5
1965 14.4
1966 16.8
1967 18.4
1968 18.6
1969 19.6
1970 18.4
1971 19.0
1972 29.4
1973 35.4
1974 29.1
1975 28.4
1976 35.6
1977 45.4
1978 50.7
1979 54.9
1980 57.0
1981 66.6
1982 69.3
1983 67.7
1984 72.8
1985 63.1
1986 61.2
1987 68.7
1988 61.9
1989 54.3
1990 39.8
1991 25.5