Year	Percent
1970	35.3562
1971	35.91731
1972	36.4557
1973	37.22084
1974	37.7129
1975	38.42482
1976	39.01869
1977	39.6789
1978	40.31532
1979	41.15044
1980	41.95652
1981	42.64392
1982	43.60587
1983	44.53608
1984	45.43611
1985	46.4
1986	47.44094
1987	48.44961
1988	49.71319
1989	50.75472
1990	52.04461
1991	53.30882
1992	54.62795
1993	56.09319
1994	57.62411
1995	59.12281
1996	60.13865
1997	61.30137
1998	62.26734
1999	63.2107
2000	64.19142
2001	65.04065
2002	65.81059
2003	66.61392
2004	67.5507
2005	68.30769
2006	68.93939
2007	69.80568
2008	70.54492
2009	71.15942
2010	71.85714
2011	72.57384
2012	73.13019
2013	73.80628
2014	74.46237
2015	75