Year	Percent
1970	44.63668
1971	44.93243
1972	45.54455
1973	45.98071
1974	46.39498
1975	46.78899
1976	47.16418
1977	47.81341
1978	48.01136
1979	48.61111
1980	49.05149
1981	49.60212
1982	50.25907
1983	50.88608
1984	51.23762
1985	51.81598
1986	52.48227
1987	53.00926
1988	53.7415
1989	54.32373
1990	55
1991	55.53191
1992	56.36743
1993	57.05521
1994	57.83133
1995	58.46457
1996	59.10853
1997	59.61905
1998	60.29963
1999	60.95764
2000	61.48282
2001	62.27758
2002	62.76224
2003	63.51119
2004	64.1286
2005	64.72546
2006	65.30278
2007	65.86151
2008	66.4557
2009	67.13396
2010	67.6876
2011	68.32579
2012	68.84273
2013	69.34307
2014	69.82759
2015	70.33898