Year	Percent
1960	64.44534
1961	64.16365
1962	64.94706
1963	64.03267
1964	64.51359
1965	63.43845
1966	61.86902
1967	59.6353
1968	54.62891
1969	53.74677
1970	52.7057
1971	50.47242
1972	54.60606
1973	53.88868
1974	38.25168
1975	48.74403
1976	51.01341
1977	55.93023
1978	54.98109
1979	51.0669
1980	64.36219
1981	62.77097
1982	62.96167
1983	60.83521
1984	65.1327
1985	63.62522
1986	58.64135
1987	61.36959
1988	66.70765
1989	60.76
1990	62.74457