1950 14.86
1955 14.94
1960 14.98
1961 15.08
1962 15.02
1963 15.02
1964 14.74
1965 14.85
1966 14.91
1967 14.98
1968 14.88
1969 15.03
1970 15.04
1971 14.89
1972 14.93
1973 15.19
1974 14.93
1975 14.95
1976 14.79
1977 15.16
1978 15.09
1979 15.14
1980 15.28
1981 15.39
1982 15.07
1983 15.29
1984 15.11
1985 15.11
1986 15.16
1987 15.32
1988 15.35
1989 15.25
1990 15.47
1991 15.41
1992 15.13
1993 15.20