Year	Percent
1970	40.75235
1971	40.85366
1972	41.66667
1973	42.02899
1974	42.37288
1975	42.97521
1976	43.43164
1977	43.86423
1978	44.52926
1979	44.91315
1980	45.52058
1981	45.99057
1982	46.77419
1983	47.41573
1984	47.92123
1985	48.50427
1986	49.16667
1987	49.89817
1988	50.59524
1989	51.35659
1990	52.08333
1991	52.86506
1992	53.61011
1993	54.41696
1994	55.09499
1995	55.81788
1996	56.52893
1997	57.28155
1998	57.93651
1999	58.63142
2000	59.14634
2001	59.79073
2002	60.41056
2003	61.15108
2004	61.72316
2005	62.27462
2006	62.94278
2007	63.58768
2008	64.07895
2009	64.68305
2010	65.18424
2011	65.75
2012	66.29766
2013	66.82809
2014	67.38095
2015	67.87808