Year	Percent
1960	9.6664
1961	9.63476
1962	9.67808
1963	9.60553
1964	9.97864
1965	11.18961
1966	11.45017
1967	12.02287
1968	12.17285
1969	12.35252
1970	11.73501
1971	11.94764
1972	13.57249
1973	14.34896
1974	26.87369
1975	22.52614
1976	29.89098
1977	21.42441
1978	28.68843
1979	22.98289
1980	42.39582
1981	27.56463
1982	29.28017
1983	22.42063
1984	24.20013
1985	29.80036
1986	25.19958
1987	33.30099
1988	23.89983
1989	30.29992
1990	15.50001