73% (1988)

69% (1987)

64% (1988)

62% (1986)

66% (1988)

65% (1990)

62% (1984)

61% (1975)

62% (1985)

60% (1978)

60% (1985)

63% (1984)

63% (1987)

58% (1980)

60% (1984)

59% (1985)

61% (1988)

56% (1986)

57% (1988)

59% (1979)