Year	Percent
1970	47.3029
1971	47.77328
1972	48.22134
1973	48.64865
1974	49.24812
1975	49.63235
1976	50.17921
1977	50.6993
1978	51.19454
1979	51.66667
1980	52.443
1981	53.01587
1982	53.72671
1983	54.24242
1984	54.73373
1985	55.49133
1986	56.21469
1987	56.90608
1988	57.83784
1989	58.31135
1990	59.27835
1991	59.94962
1992	60.83744
1993	61.68675
1994	62.35294
1995	63.36406
1996	64.18919
1997	65.12141
1998	66.09071
1999	66.80761
2000	67.70186
2001	68.42105
2002	69.24603
2003	69.90291
2004	70.72243
2005	71.64179
2006	72.39488
2007	72.98748
2008	73.68421
2009	74.35456
2010	75.04216
2011	75.70248
2012	76.17504
2013	76.78855
2014	77.3791
2015	77.94793