Year	Percent
1970	32.07547
1971	32.51534
1972	32.7381
1973	33.13953
1974	33.33333
1975	33.51648
1976	33.68984
1977	33.85417
1978	34.01015
1979	34.65347
1980	34.61538
1981	35.21127
1982	35.15982
1983	35.55556
1984	35.93074
1985	36.28692
1986	36.47541
1987	36.8
1988	36.96498
1989	37.5
1990	37.63838
1991	38.1295
1992	38.46154
1993	38.56655
1994	39.20266
1995	39.35484
1996	39.62264
1997	40.06116
1998	40.59701
1999	40.69767
2000	41.07649
2001	41.43646
2002	42.04852
2003	42.36842
2004	42.5641
2005	43.10777
2006	43.52078
2007	44.01914
2008	44.39252
2009	44.74886
2010	45.08929
2011	45.63319
2012	45.84222
2013	46.34656
2014	46.73469
2015	47.2