Year	Percent
1970	39.78873
1971	40.20619
1972	40.26846
1973	40.65574
1974	41.02564
1975	41.37931
1976	41.59021
1977	42.21557
1978	42.39766
1979	42.85714
1980	43.01676
1981	43.44262
1982	43.85027
1983	44.12533
1984	44.75703
1985	45
1986	45.47677
1987	45.80336
1988	46.24413
1989	46.66667
1990	47.19101
1991	47.57709
1992	47.94816
1993	48.41438
1994	48.86128
1995	49.39024
1996	49.8008
1997	50.39062
1998	50.76628
1999	51.31579
2000	51.84502
2001	52.44123
2002	52.83688
2003	53.48432
2004	53.84615
2005	54.43886
2006	54.93421
2007	55.41195
2008	55.94295
2009	56.45412
2010	56.94656
2011	57.57121
2012	58.02651
2013	58.61071
2014	59.09091
2015	59.5537