Year	Percent
1970	36.0515
1971	36.40167
1972	36.73469
1973	37.05179
1974	37.2093
1975	37.5
1976	38.00738
1977	38.1295
1978	38.59649
1979	38.69863
1980	39.13043
1981	39.41368
1982	39.68254
1983	40.06211
1984	40.30303
1985	40.8284
1986	40.92219
1987	41.40845
1988	41.75824
1989	42.09115
1990	42.40838
1991	42.96675
1992	43.25
1993	43.65854
1994	44.15274
1995	44.52214
1996	44.87472
1997	45.21158
1998	45.65217
1999	46.17021
2000	46.66667
2001	47.04684
2002	47.41036
2003	47.85156
2004	48.37476
2005	48.8764
2006	49.3578
2007	49.7307
2008	50.17606
2009	50.60449
2010	51.09983
2011	51.57546
2012	52.11726
2013	52.55591
2014	53.1348
2015	53.53846