1971 .1
1975 1.8
1976 2.0
1977 2.2
1978 2.5
1979 4.0
1980 6.5
1981 7.8
1982 9.1
1983 21.7
1984 25.0
1985 22.8
1986 26.0
1987 29.2
1988 33.8
1989 40.2
1990 46.5
1991 55.3
1992 57.9
1993 60.1