Year	Percent
1970	30.49327
1971	30.86957
1972	31.35593
1973	31.68724
1974	32
1975	32.55814
1976	32.83019
1977	33.33333
1978	34.1637
1979	34.48276
1980	35.2349
1981	35.50489
1982	36.2776
1983	36.80982
1984	37.5
1985	38.32853
1986	38.93557
1987	39.8374
1988	40.52632
1989	41.58163
1990	42.32673
1991	43.40528
1992	44.4186
1993	45.59819
1994	46.60832
1995	47.65957
1996	48.54772
1997	49.39271
1998	50
1999	50.7722
2000	51.50943
2001	52.21402
2002	52.88809
2003	53.53357
2004	54.32526
2005	54.82234
2006	55.55556
2007	56.00649
2008	56.6879
2009	57.25429
2010	57.95107
2011	58.47076
2012	59.20471
2013	59.68208
2014	60.28369
2015	60.86351