Year	Percent
1960	56.49515
1961	55.4441
1962	47.42196
1963	43.4954
1964	38.1677
1965	37.30951
1966	29.14348
1967	34.90684
1968	38.37893
1969	34.35396
1970	39.21268
1971	38.13445
1972	34.66318
1973	44.96038
1974	53.84593
1975	57.17563
1976	61.28536
1977	64.32939
1978	57.31283
1979	45.95938
1980	53.69803
1981	51.41575
1982	39.12295
1983	59.30088
1984	25.74633
1985	32.92379
1986	33.32983
1987	42.03097
1988	36.82298
1989	43.62344
1990	35.69261
1991	25.3466
1992	53.33727
1993	59.48454
1994	64.89045
1995	56.1473
1996	54.46299
1997	57.4782
1998	58.25449
1999	67.36314
2000	93.19641
2001	91.62902
2002	74.114
2003	72.51259
2004	73.45649
2005	75.9392
2006	51.34998
2007	49.50171
2008	54.46874
2009	53.45312
2010	58.68635
2011	72.34223
2012	74.66791
2013	65.58334
2014	71.16749
2015	63.7042
2016	56.17308
2017	55.09169