Year	Percent
1960	39.29498
1961	37.28887
1962	36.77203
1963	34.23638
1964	35.99928
1965	35.76736
1966	35.09314
1967	34.0403
1968	36.58197
1969	39.83977
1970	43.49912
1971	41.26792
1972	41.19862
1973	41.97056
1974	49.47389
1975	44.51902
1976	43.08824
1977	45.55581
1978	45.30047
1979	50.72218
1980	55.481
1981	53.72338
1982	50.13806
1983	49.68039
1984	48.94533
1985	48.01818
1986	43.07166
1987	43.28906
1988	39.30046
1989	40.0908
1990	37.85535
1991	35.10615
1992	40.12326
1993	46.52809
1994	51.27487
1995	52.1314
1996	54.91773
1997	57.62059
1998	57.27538
1999	54.98771
2000	64.15921
2001	58.70473
2002	56.86956
2003	55.9325
2004	57.40931
2005	60.78351
2006	67.68848
2007	67.24315
2008	66.34071
2009	49.20255
2010	55.81961
2011	59.7085
2012	58.25513
2013	56.30285
2014	55.42994
2015	51.75529
2016	49.64468
2017	54.77324