Year	Percent
1970	37.89474
1971	37.7551
1972	38.61386
1973	38.83495
1974	39.62264
1975	39.44954
1976	40.17857
1977	40
1978	40.67797
1979	41.32231
1980	41.6
1981	42.1875
1982	42.42424
1983	42.96296
1984	43.16547
1985	43.35664
1986	44.52055
1987	44.66667
1988	45.45455
1989	45.28302
1990	46.01227
1991	46.70659
1992	47.09302
1993	47.72727
1994	48.61878
1995	48.92473
1996	49.73822
1997	50.5102
1998	51.24378
1999	51.94175
2000	52.35849
2001	52.99539
2002	53.36323
2003	54.14847
2004	55.12821
2005	55.41667
2006	56.09756
2007	56.52174
2008	57.14286
2009	57.73585
2010	58.08824
2011	58.78136
2012	59.09091
2013	59.72696
2014	60
2015	60.58632