Year	Percent
1970	57.45614
1971	58.11966
1972	58.75
1973	59.34959
1974	59.92063
1975	60.23166
1976	61.13208
1977	61.76471
1978	62.58993
1979	63.15789
1980	63.69863
1981	64.54849
1982	65.14658
1983	65.92357
1984	66.77019
1985	67.57576
1986	68.3432
1987	69.07514
1988	70.0565
1989	70.99448
1990	71.89189
1991	72.82322
1992	73.71134
1993	74.55919
1994	75.61576
1995	76.62651
1996	77.35849
1997	78.29099
1998	78.95928
1999	79.82262
2000	80.47722
2001	81.2766
2002	81.875
2003	82.44898
2004	83
2005	83.52941
2006	84.23077
2007	84.74576
2008	85.21257
2009	85.68841
2010	86.14565
2011	86.58537
2012	87.17949
2013	87.43719
2014	87.99342
2015	88.3871