Year	Percent
1970	35.55556
1971	36.55914
1972	36.84211
1973	36.73469
1974	36.63366
1975	36.8932
1976	37.73585
1977	37.61468
1978	37.5
1979	38.26087
1980	38.13559
1981	38.84298
1982	38.4
1983	39.0625
1984	39.39394
1985	40
1986	39.56835
1987	39.86014
1988	40.41096
1989	40.66667
1990	40.90909
1991	40.8805
1992	41.71779
1993	41.91617
1994	41.86047
1995	42.61364
1996	42.54144
1997	43.24324
1998	43.15789
1999	43.58974
2000	44
2001	44.39024
2002	44.7619
2003	44.90741
2004	45.24887
2005	45.37445
2006	45.68966
2007	46.21849
2008	46.31148
2009	46.8
2010	47.26562
2011	47.52852
2012	47.95539
2013	48.18841
2014	48.58156
2015	48.78893