1971,87.9
1972,88.5
1973,88.8
1974,90.2
1975,78.1
1976,79.6
1977,81.5
1978,82.4
1979,80.5
1980,77.7
1981,76.7
1982,73.2
1983,69.3
1984,72.2
1985,76.0
1986,73.3
1987,75.0
1988,75.5
1989,77.6
1990,75.9