Year	Percent
1960	37.63708
1961	39.20601
1962	32.87666
1963	31.34537
1964	31.9399
1965	29.94642
1966	31.50596
1967	30.91599
1968	30.63735
1969	28.67586
1970	29.63894
1971	27.6028
1972	28.02824
1973	32.90547
1974	47.05053
1975	45.75181
1976	40.47192
1977	40.73513
1978	33.8276
1979	35.42661
1980	30.6368
1981	38.21078
1982	36.04384
1983	34.44613
1984	40.41221
1985	40.11665
1986	32.14954
1987	32.41863
1988	32.58472
1989	33.44199
1990	37.06746
1991	34.55743
1992	33.58244
1993	33.87408
1994	38.83818
1995	43.30996
1996	38.42549
1997	42.29352
1998	41.72346
1999	41.53533
2000	48.80942
2001	46.07753
2002	46.67182
2003	44.23115
2004	46.53571
2005	51.29664
2006	53.50116
2007	59.90554
2008	67.78986
2009	50.52391
2010	57.01998
2011	65.03486
2012	67.48773
2013	62.8702
2014	63.88913
2015	60.0781
2016	62.26612
2017	64.37324