Year	Percent
1970	47.2561
1971	47.78761
1972	48.7106
1973	49.44444
1974	50
1975	50.65274
1976	51.51515
1977	52.20588
1978	52.96912
1979	53.7931
1980	54.6875
1981	55.50756
1982	56.39413
1983	57.20081
1984	58.26772
1985	59.16031
1986	60.07394
1987	61.11111
1988	62.08696
1989	63.06914
1990	64.2623
1991	65.18283
1992	66.30603
1993	67.5188
1994	68.42105
1995	69.51567
1996	70.11173
1997	70.82192
1998	71.46703
1999	72.12682
2000	72.85714
2001	73.34184
2002	73.93484
2003	74.59926
2004	75.24272
2005	75.65632
2006	76.26322
2007	76.76301
2008	77.44875
2009	77.9148
2010	78.45304
2011	78.99891
2012	79.42122
2013	80.02114
2014	80.41667
2015	80.98664