74% (1977)

75% (1976)

77% (1981)

74% (1983)

66% (1985)

77% (1979)

74% (1984)

59% (1975)

57% (1987)

72% (1986)

76% (1984)

66% (1978)

65% (1983)

65% (1988)

60% (1989)

67% (1980)

69% (1990)

66% (1983)

67% (1985)

70% (1990)