Year	Percent
1970	41.95402
1971	41.89944
1972	42.62295
1973	42.55319
1974	43.00518
1975	43.43434
1976	43.84236
1977	44.23077
1978	44.60094
1979	45.41284
1980	45.53571
1981	46.28821
1982	46.38298
1983	46.88797
1984	47.36842
1985	47.82609
1986	48.26255
1987	49.0566
1988	49.26471
1989	50
1990	50.52632
1991	51.0274
1992	51.50502
1993	51.96078
1994	52.71565
1995	53.125
1996	53.82263
1997	54.49102
1998	54.97076
1999	55.58739
2000	56.02241
2001	56.43836
2002	56.83646
2003	57.48031
2004	58.09769
2005	58.69018
2006	59.1133
2007	59.51807
2008	59.90566
2009	60.50808
2010	61.08597
2011	61.41907
2012	62.03905
2013	62.42038
2014	62.91667
2015	63.46939