Year	Percent
1970	50.60606
1971	51.31965
1972	52.12465
1973	52.87671
1974	53.43915
1975	54.33673
1976	54.92611
1977	55.81948
1978	56.75057
1979	57.61589
1980	58.51064
1981	59.42623
1982	60.35503
1983	61.40684
1984	62.63736
1985	63.55634
1986	64.74576
1987	66.01307
1988	67.2956
1989	68.48485
1990	69.78102
1991	71.12676
1992	72.38095
1993	73.68421
1994	74.90446
1995	76.14339
1996	76.90447
1997	77.72512
1998	78.39721
1999	79.24743
2000	79.86577
2001	80.54945
2002	81.31749
2003	81.95329
2004	82.56785
2005	83.14491
2006	83.72093
2007	84.26295
2008	84.88714
2009	85.39652
2010	85.89133
2011	86.37218
2012	86.82746
2013	87.28271
2014	87.71454
2015	88.2248