Year	Percent
1970	79.51442
1971	80.05952
1972	80.61224
1973	81.11588
1974	81.62693
1975	82.25585
1976	82.61456
1977	83.20106
1978	83.78729
1979	84.22392
1980	84.66334
1981	85.31212
1982	85.83433
1983	86.33687
1984	86.72055
1985	87.20272
1986	87.77778
1987	88.33152
1988	88.77005
1989	89.29696
1990	89.80433
1991	90.30303
1992	90.88206
1993	91.35083
1994	91.89704
1995	92.33645
1996	92.8506
1997	93.33933
1998	93.80531
1999	94.16884
2000	94.60616
2001	94.94098
2002	95.34497
2003	95.7377
2004	96.0388
2005	96.32881
2006	96.69031
2007	96.96498
2008	97.23077
2009	97.49049
2010	97.81791
2011	97.99107
2012	98.2327
2013	98.54121
2014	98.70036
2015	98.92704