Year	Percent
1970	41.74312
1971	42.41071
1972	42.6087
1973	42.79661
1974	43.38843
1975	43.7751
1976	44.14062
1977	44.65649
1978	44.98141
1979	45.28986
1980	45.77465
1981	46.04811
1982	46.48829
1983	46.90554
1984	47.45223
1985	47.67802
1986	48.33837
1987	48.67257
1988	49.13793
1989	49.7191
1990	50.13699
1991	50.53476
1992	51.17493
1993	51.39949
1994	51.99005
1995	52.55474
1996	52.96912
1997	53.48837
1998	53.86364
1999	54.34298
2000	54.90196
2001	55.22388
2002	55.74113
2003	56.03272
2004	56.62651
2005	57.08661
2006	57.52896
2007	57.84499
2008	58.25603
2009	58.65209
2010	59.21288
2011	59.57821
2012	60
2013	60.50847
2014	60.8985
2015	61.27451