Year	Percent
1960	12.71526
1961	15.99705
1962	12.79403
1963	15.86887
1964	15.98045
1965	17.15206
1966	14.95866
1967	13.65065
1968	14.89257
1969	15.98973
1970	11.51359
1971	13.26103
1972	15.73721
1973	13.90939
1974	17.4628
1975	12.46312
1976	10.03384
1977	20.26162
1978	25.84037
1979	24.30542
1980	33.17984
1981	24.82087
1982	25.96804
1983	23.62724
1984	14.58875
1985	6.33013
1986	6.9635
1987	6.69068
1988	4.82254
1989	7.68308
1990	9.78675
2013	14.53067
2014	14.38242
2015	15.65241
2016	15.10816
2017	13.4626