Year	Percent
1970	50
1971	50.4065
1972	50.79365
1973	50.96525
1974	51.69811
1975	51.83824
1976	52.32975
1977	52.44755
1978	52.90102
1979	53.33333
1980	53.57143
1981	54.28571
1982	54.48916
1983	54.98489
1984	55.16224
1985	55.6196
1986	55.89888
1987	56.31868
1988	56.83646
1989	57.06806
1990	57.54476
1991	58
1992	58.19071
1993	58.47255
1994	59.11215
1995	59.36073
1996	59.59821
1997	60.17505
1998	60.59957
1999	61.00629
2000	61.3963
2001	61.84739
2002	62.20472
2003	62.62042
2004	63.138
2005	63.51852
2006	63.88385
2007	64.41281
2008	64.74695
2009	65.23973
2010	65.71429
2011	66.17162
2012	66.66667
2013	67.09062
2014	67.5507
2015	67.99387